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Strengthen

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Question 21Question →

Each of the arguments below arrives at a causal conclusion based on an observed correlation or trend. Match each argument with the evidentiary statement that most strongly strengthens its conclusion by ruling out a key rival hypothesis.

Click a left item, then click its matching right item

Items

Paleoclimatologists detected a sharp spike in micro-charcoal particles in Andean ice cores dating to the late sixth century. They concluded that widespread agricultural burning by the Tiwanaku civilization caused this atmospheric particulate peak.
Marine biologists recorded a steady rise in the pitch and volume of beluga whale contact calls in a busy shipping estuary over five years. They concluded that the whales altered their vocal acoustics specifically to overcome masking noise from commercial ships.
Corporate auditors using newly introduced automated risk-flagging software approved significantly more non-compliant transactions during the final two hours of their shifts than during early hours. Researchers concluded that interaction with the software accelerated cognitive fatigue.

Matches

Show answer & explanation

Answer

Argument 1 (Tiwanaku agricultural burning) matches the regional lake sediment finding ruling out natural wildfires; Argument 2 (Beluga whale acoustic shifts) matches the isolated fjord control group showing unchanged vocal patterns; Argument 3 (Auditor software fatigue) matches the manual review control group showing no late-shift error escalation.
Each correct pairing matches an argument with an empirical finding that eliminates an unstated confounding factor. For the Tiwanaku argument, ruling out natural wildfires and regional droughts establishes anthropogenic burning as the probable source of the micro-charcoal. For the beluga whale argument, observing stable vocal patterns in an unexposed control population confirms that shipping noise—rather than aging or water conditions—drove the acoustic adaptation. For the audit software argument, demonstrating that manual reviewers on identical shifts did not experience late-shift accuracy decline isolates the software tool as the driver of performance degradation.

Step-by-Step Solution

1
Analyze each argument's causal conclusion and identify its primary unstated gap or rival explanation.
Identified three distinct gaps: (1) charcoal could stem from natural wildfires; (2) vocal shifts could stem from demographic or environmental factors; (3) auditor errors could stem from standard end-of-shift tiredness independent of software.
Strengthening a causal claim requires finding evidence that rules out plausible alternative causes or provides a parallel control condition.
2
Evaluate the evidentiary statements to determine which finding eliminates each argument's specific alternative cause.
The sediment data eliminates the natural wildfire explanation for Argument 1; the vessel-free fjord population isolates shipping noise for Argument 2; the manual auditing baseline isolates the software interface for Argument 3.
Each correct match provides a valid control or eliminates a confounding variable directly tied to the corresponding argument.
3
Verify that no matched evidentiary statement introduces irrelevant scope or weakens any paired conclusion.
Each pair establishes a robust, non-overlapping causal strengthener.
Ensures full logical consistency across all pairs.

Key Concept

Strengthening Causal Claims via Control Groups and Alternative Hypothesis Elimination
Question 22Question →

Agricultural Scientist: In a field trial across thirty commercial apple orchards, trees treated with a foliar spray containing live *Bacillus* bacteria produced fruit with significantly lower rates of bitter rot fungal infection than untreated trees did. Because chemical analyses revealed that the spray did not alter the thickness or acidity of the apple skin, the scientist concluded that the *Bacillus* bacteria themselves actively suppress the germination of bitter rot fungal spores on the fruit's surface.

Which of the following, if true, most strengthens the agricultural scientist's argument?

Show answer & explanation

Answer: Trees sprayed with a sterile solution identical to the foliar spray in every respect except lacking live *Bacillus* bacteria experienced rates of bitter rot infection comparable to those of untreated trees.

Answer

The statement showing that trees sprayed with a sterile solution containing all spray ingredients except the live bacteria suffered infection rates comparable to untreated trees.
The argument concludes that live *Bacillus* bacteria were the direct cause of the lower infection rates. A major vulnerability of this inference is that the liquid spray itself or other inactive carrier ingredients might have washed away spores or created a hostile environment. By showing that an identical spray without live bacteria yields infection rates no better than no treatment at all, the correct choice acts as a negative control, ruling out the carrier solution as an alternative cause and strongly reinforcing the causal role of the bacteria.

Step-by-Step Solution

1
Identify the premises and conclusion of the argument.
Premise: Apple trees sprayed with a bacterial mixture had lower bitter rot infection rates than untreated trees, without changes to apple skin thickness or acidity. Conclusion: The live bacteria themselves actively suppress fungal spore germination.
Clarifying the boundary between observed evidence and the causal claim reveals the reasoning gap.
2
Isolate the unstated assumption and potential alternative explanations.
The author assumes that no other element of the foliar spray application (such as the liquid carrier, surfactant, or physical moisture) caused the reduction in fungal infection.
Causal conclusions in experimental settings require establishing that the proposed independent variable, rather than confounding treatment factors, generated the outcome.
3
Evaluate the answer choices for information that eliminates confounding variables or substantiates the causal link.
Demonstrating that an identical spray lacking only the bacteria produces no therapeutic effect confirms that the bacteria are necessary for the observed protection.
Ruling out a potential alternative cause directly strengthens a causal argument.

Key Concept

Causal strengthening via ruling out confounding variables and establishing negative controls
Estimated Time:1m 15s
Question 23Question →

Each of the following arguments draws a causal or explanatory conclusion from empirical observations. Match each argument with the supplementary finding that most strengthens its conclusion.

Click a left item, then click its matching right item

Items

Paleoclimatologist: Ice core strata from an Antarctic dome reveal an abrupt surge in atmospheric methane concentrations coinciding with a rapid deglacial warming episode 14,700 years ago. Because isotopic examination of this trapped gas reveals a depleted carbon-14 profile characteristic of biogenic decomposition in tropical wetlands rather than marine methane hydrates, wetland methane release must have been the primary catalyst that initiated the warming episode.
Behavioral Economist: In a municipal workplace study, workers automatically enrolled in emergency savings accounts accumulated three times more savings over twelve months than workers who were required to actively opt in, even though both groups completed the same mandatory financial literacy curriculum. Because both cohorts scored identically on post-curriculum comprehension assessments, the higher accumulation among automatically enrolled workers must be attributable entirely to behavioral inertia rather than disparities in financial literacy.
Plant Biologist: *Arenaria aggregata*, a cushion plant inhabiting exposed subalpine ridgelines, produces leaf cuticles with forty percent greater tensile strength than those of closely related lowland taxa. Because gale-force winds are frequent along these ridgelines whereas herbivorous insect populations are virtually nonexistent at these elevations, this reinforced cuticle must have evolved primarily to prevent mechanical damage from wind rather than to resist herbivory.

Matches

Show answer & explanation

Answer

The paleoclimatologist's argument matches with the chronological finding placing the methane surge before the warming; the behavioral economist's argument matches with the finding confirming opt-in workers did not save more in external accounts; and the plant biologist's argument matches with the experimental evidence showing unreinforced plants suffer reproductive failure under high winds.
Each matched pair correctly resolves the distinct inferential vulnerability of the stimulus. For the paleoclimatological claim, demonstrating that the methane surge preceded warming by decades validates the causal direction and rules out reverse causality. For the economic study, auditing external accounts eliminates the primary alternative explanation that opt-in workers saved outside the workplace program. For the botanical claim, demonstrating that wind stress inflicts structural damage and fitness loss on unreinforced plants directly substantiates the claim that the trait evolved as an adaptation to mechanical wind forces.

Step-by-Step Solution

1
Analyze the paleoclimatologist's argument to locate the core vulnerability in the causal claim.
The argument concludes that wetland methane caused the deglacial warming episode based on isotopic signature. The unstated gap is the temporal order of cause and effect—whether the methane surge initiated warming or was triggered by pre-existing warming.
Strengthening a causal initiation claim requires establishing that the purported cause preceded the effect.
2
Analyze the behavioral economist's argument to identify unaddressed alternative hypotheses.
The conclusion claims that differences in program savings were caused entirely by enrollment inertia. The unaddressed possibility is that opt-in workers saved equivalent amounts in outside accounts.
Strengthening an attribution of an observed disparity to a specific mechanism requires ruling out competing behavioral substitutions.
3
Analyze the plant biologist's argument to assess the functional evolutionary claim.
The conclusion asserts that cuticular tensile strength is an adaptation to wind stress. The gap is whether ambient wind forces actually impose selection pressure against unreinforced leaves.
Strengthening an evolutionary adaptation argument requires demonstrating that the absence of the trait reduces fitness under the specified environmental stressor.
4
Match each argument with its corresponding uniquely supportive evidentiary statement.
The methane argument pairs with the stratigraphic sequence dating; the workplace savings argument pairs with the external account audit; the alpine plant argument pairs with the simulated wind stress experiment on lowland relatives.
Each statement directly resolves the primary vulnerability of its respective argument without providing relevant support to the other scenarios.

Key Concept

Strengthening causal and explanatory arguments through chronological validation, elimination of competing explanations, and demonstration of selective mechanisms
Estimated Time:2m 0s
Question 24Question →

Public Health Official: A ten-year study found that adults consuming over 400 milligrams daily of compound Q—a synthetic preservative in processed foods—had a 40 percent higher incidence of chronic kidney disease (CKD) than those consuming under 50 milligrams daily. The authors concluded that compound Q directly causes CKD. This is highly suspect. Compound Q is prevalent in convenience foods heavily relied upon by people in "food deserts" lacking fresh produce. Residing in a food desert correlates strongly with lower socioeconomic status (SES), which is a major independent risk factor for CKD. Therefore, the higher CKD incidence among heavy compound Q consumers is almost certainly a byproduct of SES disparities rather than the chemical itself.

Which of the following, if true, most strongly supports the public health official's conclusion?

Show answer & explanation

Answer: Among study participants belonging to the same socioeconomic bracket, those who consumed more than 400 milligrams of compound Q daily did not exhibit a higher incidence of CKD than those who consumed less than 50 milligrams daily.

Answer

The statement showing that within the same socioeconomic bracket, varying levels of compound Q consumption do not change the incidence of CKD.
The public health official argues that a correlation between compound Q and CKD is actually driven by a third confounding variable: socioeconomic status (SES). To strengthen this claim, one must demonstrate that compound Q has no causal power independent of SES. The correct answer achieves this by holding SES constant; it shows that among people with the same SES, consuming large amounts of compound Q does not lead to higher rates of CKD. This isolates the variables and proves that the original correlation was indeed merely a byproduct of SES disparities.

Step-by-Step Solution

1
Analyze the logical structure of the stimulus.
Identify the conclusion: The higher CKD incidence is caused by SES disparities, not compound Q. Identify the premises: The study shows a correlation between compound Q and CKD. However, heavy compound Q consumers live in food deserts, which correlates with low SES, a known independent risk factor for CKD.
Understanding the exact causal claim being made is necessary before attempting to strengthen it.
2
Identify the reasoning gap or causal vulnerability.
The official assumes that just because a plausible alternative cause (SES) exists, the original proposed cause (compound Q) must be blameless. To strengthen this, evidence must be found that isolates the variables and proves compound Q is indeed harmless.
Strengthening a claim of an alternative cause often requires demonstrating that when the alternative cause is controlled for, the original correlation disappears.
3
Evaluate the options against the identified logical gap.
The correct option must hold the confounding variable (SES) constant. The option stating that participants in the same SES bracket showed no difference in CKD rates regardless of compound Q consumption achieves exactly this.
This rules out compound Q as the active causal agent, completely validating the official's alternative causal hypothesis.

Key Concept

Causal Reasoning: Alternative Causes and Controlling Variables
Question 25Question →

Marine archaeologists examining ancient wooden shipwrecks in the Black Sea observed that wrecks resting at depths greater than 150 meters show virtually no degradation from *Teredo navalis* (a wood-boring mollusk), whereas wrecks at shallower depths in the same sea are severely degraded. Because the water in the Black Sea below 150 meters is permanently devoid of dissolved oxygen (anoxic), whereas shallower water contains normal oxygen levels, the archaeologists concluded that the absence of dissolved oxygen is the primary factor preventing the mollusks from colonizing and destroying the deep-water wrecks.

Which of the following, if true, most strengthens the marine archaeologists' argument?

Show answer & explanation

Answer: Specimens of *Teredo navalis* placed in water samples drawn from below 150 meters in the Black Sea survive and consume wood normally, provided that dissolved oxygen is continuously introduced into the water.

Answer

The argument is most strengthened by the finding that *Teredo navalis* can survive and consume wood in water drawn from below 150 meters in the Black Sea as long as dissolved oxygen is artificially added.
The correct response demonstrates that when oxygen is artificially supplied to deep Black Sea water, *Teredo navalis* behaves normally. This experimental control eliminates alternative hypotheses (such as toxic minerals, extreme pressure, or salinity differences unique to the deep basin) that could otherwise account for the absence of wood degradation, thereby directly strengthening the conclusion that oxygen deprivation is the operative factor.

Step-by-Step Solution

1
Analyze the argument's structure, premises, and conclusion.
Premise: Deep-water wrecks (>150m) in the Black Sea lack mollusk degradation and lack dissolved oxygen, whereas shallow wrecks have both. Conclusion: The lack of dissolved oxygen is the primary factor preventing mollusk degradation in deep waters.
Identifying the exact causal link claimed by the author exposes the underlying gap.
2
Identify the primary inferential gap or vulnerability.
The argument assumes that anoxia itself is the cause, overlooking potential confounding variables inherent to deep Black Sea water (e.g., salinity, pressure, temperature, or other chemical inhibitors).
To strengthen a causal claim, one must either eliminate alternative causes, demonstrate the causal mechanism, or show that the effect occurs when the cause is present and vanishes when the cause is absent.
3
Evaluate the answer choices to determine which best bridges this gap.
The statement showing that mollusks flourish in deep Black Sea water when oxygen is introduced isolates oxygen deficiency as the sole barrier, ruling out other chemical or biological deterrents.
This controlled experimental finding directly substantiates the proposed causal relationship.

Key Concept

Strengthening Causal Attribution by Ruling Out Confounding Variables
Estimated Time:2m 0s
Question 26Question →

Paleoanthropologist: Excavations at the Upper Paleolithic site of Ghor-A revealed that microlithic stone bladelets bearing microscopic traces of conifer resin were concentrated exclusively around Hearth 3, where reindeer faunal remains were clustered, and were entirely absent around Hearth 1, where grinding stones and plant processing tools predominated. Because conifer resin was widely utilized during this era as an adhesive to attach stone tips to wooden spear shafts, the occupants of Ghor-A must have used Hearth 3 specifically as a designated workshop for assembling projectile hunting weaponry rather than for general culinary preparation.

Evaluate the following statement as True or False:

The discovery that unworked wood shavings, burnt shaft fragments, and debitage from bladelet manufacturing were recovered in dense concentrations surrounding Hearth 3 but nowhere else at Ghor-A strengthens the paleoanthropologist's argument.

Show answer & explanation

Answer: True

Answer

True
The claim is true because finding manufacturing debitage, burnt shaft fragments, and wood shavings localized at Hearth 3 directly corroborates the hypothesis that projectile weaponry was manufactured and hafted at that location, thereby eliminating the alternative explanation that the resinous bladelets were used elsewhere and merely discarded near cooking refuse.

Step-by-Step Solution

1
Analyze the structure of the argument in the stimulus
Premises: Resinated bladelets and reindeer bones are found only at Hearth 3; conifer resin was used as spear-hafting adhesive. Conclusion: Hearth 3 was specifically used as a workshop for assembling hunting weapons.
Identifying the conclusion and the supporting premises isolates the logical gap between finding adhesive-coated bladelets and inferring that full weapon manufacturing took place at that specific hearth.
2
Evaluate the impact of the supplementary statement
The statement introduces additional direct evidence of projectile manufacture (shaft wood shavings, burnt shaft fragments, and manufacturing debitage) restricted to Hearth 3.
A strengthener must increase the plausibility of the conclusion by bridging an assumption or adding independent support for the claimed activity.
3
Determine whether the statement bolsters the argument
The statement provides decisive corroboration of weapon assembly at Hearth 3, confirming that the statement accurately describes a strengthening effect.
Since the evidence reinforces the author's causal and functional inference, classifying the statement as strengthening the argument is correct (True).

Key Concept

Strengthening a functional/causal attribution by providing corroborating physical evidence of the hypothesized activity
Estimated Time:1m 15s
Question 27Question →

A recent municipal study observed that neighborhoods with a high density of street-side flower beds experienced significantly fewer occurrences of public littering than neighborhoods with few or no flower beds. The city planning board concluded that the presence of well-maintained flower beds directly encourages residents and visitors to dispose of their trash properly.

Which of the following, if true, most strongly supports the city planning board's conclusion?

Show answer & explanation

Answer: When flower beds were introduced into several previously barren neighborhoods, the volume of litter discarded on those streets declined noticeably even though municipal street sweeping frequency remained unchanged.

Answer

Evidence demonstrating that introducing flower beds to barren neighborhoods led to a decline in litter while cleaning frequency stayed the same most strongly supports the conclusion.
The argument concludes that the presence of flower beds directly causes individuals to litter less. The correct response strengthens this claim by presenting a controlled scenario: when flower beds were added to neighborhoods that previously lacked them, littering decreased even though the frequency of street sweeping remained unchanged. This demonstrates the effect following the introduction of the cause while ruling out an alternative explanation.

Step-by-Step Solution

1
Identify the core premises and conclusion in the stimulus
Premise: Neighborhoods with flower beds have less litter. Conclusion: Flower beds directly cause people to dispose of trash properly.
Strengthening requires identifying the exact causal relationship the author attempts to establish.
2
Identify the reasoning gap or potential weaknesses
The argument assumes that the flower beds themselves caused the reduction in litter, rather than an unstated third factor (such as extra cleaning or more trash cans).
A valid strengthener will either provide direct evidence of causality or eliminate an alternative explanation.
3
Evaluate the answer choices for positive impact on the conclusion
The statement showing a before-and-after reduction in litter following the addition of flower beds while holding street cleaning constant directly validates the causal link.
Demonstrating that the effect occurs specifically when the cause is introduced reinforces the board's conclusion.

Key Concept

Causal Strengthening and Controlling for Confounding Variables
Estimated Time:1m 0s
Question 28Question →

Match each brief argument with the statement that most effectively strengthens its conclusion.

Click a left item, then click its matching right item

Items

A study found that employees who participated in morning exercise sessions reported less back pain than non-participants. The wellness director concluded that morning exercise sessions directly reduce back pain.
A survey of 200 science majors found that over 80 percent preferred digital textbooks to printed textbooks. Based on this finding, the campus bookstore concluded that university students in general prefer digital textbooks.
A delivery company plans to replace its gasoline vans with electric vans, concluding that this change will decrease total vehicle operational costs because electricity costs less per mile than gasoline.

Matches

Show answer & explanation

Answer

The exercise study argument matches the statement ruling out baseline health differences among participants; the textbook survey argument matches the statement confirming sample representativeness across disciplines; and the electric van argument matches the statement ensuring maintenance expenses do not exceed fuel savings.
Each correct pairing provides evidence that directly resolves the central assumption of its matched argument: eliminating selection bias supports causal attribution, confirming sample typicality supports generalization, and bounding auxiliary expenses supports net cost reduction.

Step-by-Step Solution

1
Analyze the reasoning gap in each argument.
The exercise argument assumes correlation implies causation without ruling out selection bias; the bookstore argument assumes a specific subgroup represents the whole student body; the delivery company argument assumes fuel savings translate to total operational cost reduction without considering other vehicle expenses.
Identifying the unstated assumption or vulnerability in each argument is necessary to determine what information will strengthen it.
2
Evaluate each potential strengthener against the identified gaps.
Eliminating alternative baseline causes strengthens the causal claim; establishing cross-major consistency strengthens the inductive generalization; bounding ancillary maintenance costs strengthens the total expense claim.
A valid strengthener directly addresses and mitigates the specific logical vulnerability of its target argument.
3
Pair each argument with its corresponding strengthening claim.
Each argument is uniquely paired with the evidence that directly substantiates its specific assumption.
Ensures an exact one-to-one logical correspondence between the arguments and supporting statements.

Key Concept

Strengthen reasoning: Identifying and bridging distinct logical gaps, including eliminating confounding variables in causal arguments, establishing sample representativeness in generalizations, and accounting for net variables in financial arguments.
Question 29Question →

Agronomists observed that blueberry plots treated with crushed pecan shell mulch produced 25 percent higher fruit yields than untreated bare soil plots. The agronomists concluded that nutrients released into the soil by decomposing pecan shells caused the increase in yield.

True or False: The finding that blueberry plots covered with an inert synthetic ground cover—which provides identical moisture retention and weed suppression to pecan shells but releases zero nutrients—produced yields no higher than untreated bare soil plots strengthens the agronomists' argument.

Show answer & explanation

Answer: True

Answer

True
The claim is evaluated as True because the supplementary finding functions as a negative control. By showing that the yield gain does not occur under identical non-nutritive physical conditions, the finding eliminates moisture retention and weed suppression as alternate causes, directly boosting the plausibility of the nutrient-based explanation.

Step-by-Step Solution

1
Identify the conclusion and premises in the argument.
Premise: Blueberry plots with pecan shell mulch yielded 25% more fruit than bare soil. Conclusion: Nutrients from decomposing pecan shells caused the yield increase.
Clarifying the core claim isolates the exact causal relationship that must be supported.
2
Identify the unstated assumption and potential alternative explanations.
The argument assumes that non-nutritional properties of the mulch (such as weed control or moisture retention) were not the true causes of the increased yield.
Causal arguments on the LSAT are vulnerable to alternate causes; eliminating an alternate cause strengthens the conclusion.
3
Evaluate the impact of the supplementary statement.
The statement acts as a control test showing that when physical benefits are present without nutrients, yield does not increase.
Eliminating alternative mechanisms validates the author's proposed causal factor, confirming that the statement strengthens the argument.

Key Concept

Strengthening a causal conclusion by ruling out alternative explanations through a control condition
Estimated Time:45s
Question 30Question →

Match each short argument on the left with the additional premise on the right that most effectively strengthens its conclusion.

Click a left item, then click its matching right item

Items

A local bakery began using organic stone-ground flour and saw a 30% rise in pastry sales over two months, concluding that customers prefer the flavor of stone-ground flour.
A community center introduced fifteen-minute morning stretching sessions and recorded improved punctuality among attendees, concluding that stretching directly motivates people to arrive on time.
A veterinary clinic began playing soft instrumental music in its lobby and reported fewer behavioral signs of anxiety in pets, concluding that the music pacified the animals.

Matches

Show answer & explanation

Answer

Match the bakery argument with the premise ruling out pricing and marketing changes; match the community center argument with the premise ruling out transit and parking changes; and match the veterinary clinic argument with the premise establishing reduced anxiety specifically during active music playback.
Each correct pair matches an inductive causal conclusion with a supplementary fact that either eliminates alternative explanations (such as pricing/marketing for the bakery, or transit conditions for the community center) or demonstrates that the effect occurs when the cause is present and does not occur when the cause is absent (for the veterinary clinic).

Step-by-Step Solution

1
Identify the causal conclusion and unstated assumptions in each left-hand argument.
Each argument concludes that a specific intervention caused an observed improvement, assuming no unmentioned confounding variables or alternative explanations accounted for the change.
Strengthening a causal argument typically requires eliminating plausible alternative causes or demonstrating that the effect correlates directly with the presence of the cause.
2
Evaluate the right-hand options for evidence that controls for confounding variables or establishes covariation.
The statement holding bakery prices and advertising constant eliminates rival explanations for sales; the statement holding transit and parking constant eliminates rival explanations for punctuality; and the statement comparing music to silence shows direct covariation of cause and effect.
Matching each premise to its corresponding context links each specific gap to its appropriate validation.
3
Form the correct pairs based on matching each argumentative gap to its resolving evidence.
All three arguments are paired with statements that specifically support their respective causal conclusions.
Confirming each pair ensures precise alignment without cross-matching contexts.

Key Concept

Strengthening Causal Arguments by Ruling Out Confounding Variables and Demonstrating Covariation
Estimated Time:1m 0s
Question 31Question →

Paleoecologists analyzing sediment cores from Lake Kerinci observed an abrupt collapse in endemic broadleaf canopy pollen approximately 4,200 years ago, coinciding precisely with a massive spike in micro-charcoal deposits. Because micro-charcoal is a definitive indicator of intense forest fires, the researchers concluded that widespread wildfires triggered by regional drought were the direct cause of the broadleaf canopy collapse.

Statement: Fossilized pollen records from nearby, hydrologically isolated basins that experienced the same regional drought but lacked charcoal deposits show that broadleaf canopy tree populations remained stable during that period; this finding strengthens the researchers' conclusion.

Show answer & explanation

Answer: True

Answer

True. The supplementary finding strengthens the argument by establishing a control condition that isolates wildfire as the necessary causal agent of the tree population collapse.
The conclusion asserts a specific causal attribution: wildfires caused the collapse of broadleaf trees. A central weakness in such arguments is the presence of confounding variables (e.g., the drought itself could have dehydrated and killed the trees directly, with fires acting merely as an incidental byproduct). The supplementary finding introduces a classic negative control: where the drought was present but fire was absent, the trees survived. Demonstrating that the effect disappears when the proposed cause is removed strongly substantiates the causal link.

Step-by-Step Solution

1
Deconstruct the stimulus argument into premises, conclusion, and unstated causal assumptions.
Premises: 4,200 years ago, broadleaf pollen sharply declined while micro-charcoal (wildfire indicator) spiked. Conclusion: Wildfires triggered by drought directly caused the broadleaf collapse. Unstated Gap: Assumes the drought itself, or another drought-related factor, did not directly kill the trees independently of the fire.
Identifying the causal gap reveals what evidence is required to bolster the link between wildfire and canopy collapse.
2
Evaluate the logical effect of introducing the supplementary evidence.
The evidence shows that in areas where drought occurred without wildfires, broadleaf canopy trees did not collapse.
This comparative control demonstrates that the effect (collapse) does not occur in the absence of the hypothesized cause (wildfire), ruling out the rival hypothesis that drought alone caused the extinction.
3
Determine the truth value of the evaluation statement.
Because ruling out a major alternative explanation and establishing a control group strengthens a causal conclusion, the statement asserting that the finding strengthens the conclusion is True.
Affirms the correct evaluation of the logical support provided.

Key Concept

Strengthening Causal Claims through Control Comparison and Ruling Out Alternative Causes
Estimated Time:2m 0s
Question 32Question →

Entomologists studying leafcutter ants (*Atta cephalotes*) observed that worker ants harvest fresh leaves to nourish their symbiotic fungal gardens (*Leucoagaricus gongylophorus*). When foragers supply leaves containing chemical compounds that inhibit fungal development, the colony completely ceases collecting foliage from that specific plant species within two days, even though the worker ants themselves suffer no toxic effects from the plant. The entomologists hypothesize that the cultivated fungus emits chemical signaling molecules that condition the ants to discontinue harvesting harmful vegetation.

Statement: The finding that worker ants persist in collecting toxic leaves when supplied with fungal gardens whose chemical secretions are chemically inhibited, even as the fungal garden suffers visible tissue necrosis, provides logical support for the entomologists' hypothesis.

Show answer & explanation

Answer: True

Answer

True, because establishing that blocking fungal chemical secretions prevents the foraging change despite visible fungal decay confirms chemical signaling as the governing causal mechanism and eliminates the competing explanation of physical observation.
The statement is correct because the described experimental finding demonstrates that blocking chemical secretion prevents the avoidance behavior despite the presence of visible fungal damage. This confirms that chemical cues are the active mechanism and eliminates the alternative explanation that ants react directly to physical deterioration.

Step-by-Step Solution

1
Identify the argument's premises and the central hypothesis.
Premise: Worker ants stop gathering toxic leaves within 48 hours despite being immune to the plant toxins. Hypothesis: The fungus produces chemical signals that condition the ants to avoid the plant.
Understanding the precise causal link asserted between fungal chemical emissions and ant behavioral change is necessary to evaluate supportive evidence.
2
Analyze the reasoning gap and potential alternative explanations.
The argument assumes that chemical cues, rather than visual or physical cues of fungal damage, trigger the ants' avoidance behavior.
Strengthening a causal claim requires providing evidence that validates the specific mechanism or rules out alternative triggers.
3
Evaluate the impact of the supplementary statement.
When chemical cues are blocked, avoidance fails to occur even though visible necrosis is present, proving chemical cues are necessary and that physical necrosis alone does not trigger avoidance.
This experimental control isolates the chemical variable and eliminates the rival hypothesis of visual or structural cues, thereby strengthening the hypothesis.

Key Concept

Causal strengthening via control of alternative mechanisms
Question 33Question →

Match each argument on the left with the evidentiary finding on the right that most effectively strengthens its central conclusion.

Click a left item, then click its matching right item

Items

Agronomists noted that apple orchards sprayed with zinc oxide nanoparticles showed significantly lower rates of calcium-deficiency disorders than untreated orchards, and concluded that the nanoparticles enhance root-to-fruit calcium transport.
Biologists observed that coyotes inhabiting areas near major highway corridors maintain home ranges 40 percent smaller than forest-dwelling coyotes, and concluded that traffic noise restricts their territorial movement.
Researchers found that early childhood bilinguals outperformed late bilinguals on non-verbal executive control tasks, concluding that early dual-language acquisition directly reinforces domain-general inhibitory neural circuits.

Matches

Show answer & explanation

Answer

Match left_1 (apple orchard calcium transport) to right_1 (phloem sap calcium mobility), left_2 (coyote territory size and traffic noise) to right_2 (range expansion upon noise dampening), and left_3 (early bilingualism and inhibitory circuits) to right_3 (longitudinal prefrontal growth following immersion).
Each evidentiary finding directly substantiates the core causal mechanism asserted in the corresponding argument. For the agricultural argument, showing increased calcium mobility in the phloem while soil levels remain constant confirms the internal transport mechanism. For the ecological argument, showing territory expansion when noise is mitigated isolates acoustic disturbance from physical highway boundaries. For the cognitive argument, showing structural prefrontal changes after language exposure against a control group confirms the developmental causality.

Step-by-Step Solution

1
Identify the causal hypothesis and unstated assumptions in each argument on the left.
Argument 1 posits nanoparticle-induced internal transport; Argument 2 posits acoustic noise as the behavioral constraint; Argument 3 posits early language acquisition as the neurodevelopmental cause.
Strengthening an argument requires finding evidence that substantiates the proposed causal mechanism or rules out confounding factors.
2
Evaluate the evidentiary findings on the right to match each with its corresponding causal claim.
Finding 1 validates internal mobilization; Finding 2 isolates acoustic disturbance using a natural control; Finding 3 provides longitudinal neural imaging data tied to immersion onset.
Each strengthener addresses the specific inferential gap and potential alternative explanations of its respective argument.
3
Verify that each pair is uniquely linked and that no cross-application creates ambiguity.
Each domain (agronomy, wildlife ecology, cognitive neuroscience) maps uniquely and unequivocally to its corresponding evidentiary finding.
Ensures unambiguous, logically sound matching across all pairs.

Key Concept

Strengthening causal arguments by corroborating the mechanism of action or controlling for confounding variables.
Question 34Question →

To reduce light pollution, several rural resort towns recently replaced conventional globe streetlights with full-cutoff fixtures, which direct all emitted light downward. Over the two years following the replacement, evening retail sales in the commercial centers of these towns rose by 14 percent, while evening sales in neighboring towns that retained conventional lighting remained unchanged. Researchers concluded that the clearer view of the night sky created by the reduced upward glare made evening strolls through commercial districts more attractive to visitors, leading to increased retail spending. Which of the following, if true, most strongly supports the researchers' conclusion?

Show answer & explanation

Answer: In the towns that installed the full-cutoff fixtures, the increase in evening retail sales occurred almost entirely on clear nights rather than on overcast nights when the stars were obscured.

Answer

The statement showing that the increase in evening retail sales in the towns with new fixtures was concentrated on clear nights rather than overcast nights.
The correct response provides strong empirical support for the causal hypothesis by demonstrating covariation between the purported cause and the observed effect. If the sales increase occurred almost exclusively when the night sky was actually visible (clear nights) and disappeared when the view was blocked by clouds (overcast nights), it directly confirms that the aesthetic enjoyment of the night sky—rather than some constant feature like fixture shape or everyday downward lighting—was the operative factor behind the retail growth.

Step-by-Step Solution

1
Identify the premises and conclusion of the argument.
Premise: Replacing globe lights with full-cutoff fixtures correlated with a 14% increase in evening retail sales, while towns without the change saw flat sales. Conclusion: The improved visibility of the night sky caused visitors to find evening strolls more attractive, which drove the retail spending increase.
Isolating the conclusion reveals that the core reasoning relies on a specific causal attribution.
2
Identify the logical vulnerability or unstated gap in the causal claim.
The author assumes that night sky visibility itself caused the spending increase, rather than other factors associated with the fixture change (e.g., ground illumination, general economic shifts, or safety improvements).
Strengthening a causal argument requires corroborating the proposed mechanism, showing covariation, or ruling out alternative causes.
3
Evaluate the answer choices for evidence that strengthens the link between night sky visibility and retail spending.
Showing that the sales surge occurred specifically on clear nights (when the night sky was visible) and not on overcast nights (when the night sky was blocked) confirms that the effect is tied to the proposed cause.
Demonstrating that the effect is present when the cause is present and absent when the cause is absent directly reinforces causal validity.

Key Concept

Causal Strengthening via Covariation (Presence/Absence of Cause and Effect)
Estimated Time:1m 15s
Question 35Question →

Consider the following argument:

Ecologist: Over the past fifty years, the upper treeline of mountain birch forests in the Scandes range has shifted upward by an average of eighty meters. While many researchers attribute this migration entirely to rising regional summer temperatures prolonging the vegetative growing season, birch seedling survival at the alpine margin is primarily limited by herbivory from mountain hare populations rather than by cold temperatures. Because regional wildlife monitoring records confirm that mountain hare populations in these specific valleys experienced a sharp, sustained collapse starting sixty years ago, this release from seedling herbivory, rather than climatic warming, is the principal cause of the treeline ascent.

Statement: If true, the discovery that in adjacent valleys where mountain hare populations remained stable under hunting bans, the mountain birch treeline did not advance upward over the past fifty years despite experiencing identical increases in summer temperatures, strengthens the ecologist's argument.

Show answer & explanation

Answer: True

Answer

True (The supplementary finding strengthens the ecologist's argument by providing a controlled comparison that rules out temperature increases as the sole cause and isolates hare population decline as the operative factor).
The statement is true because the finding functions as a natural control experiment. By showing that in valleys where hare populations did not collapse, identical temperature increases failed to produce treeline advancement, the evidence directly refutes the rival hypothesis that warming alone drove the ecological shift and confirms that the decline in herbivory was an indispensable causal factor.

Step-by-Step Solution

1
Analyze the stimulus structure, identifying premises, competing causes, and the conclusion.
The ecologist concludes that release from hare herbivory, rather than rising summer temperatures, is the principal cause of the 80-meter treeline ascent in the Scandes range.
Deconstructing the causal claim clarifies that the author must defend hare reduction as the operative cause while discounting climate warming as the primary driver.
2
Assess the logical impact of the supplementary statement.
The statement introduces a natural control group: valleys with identical warming but stable hare populations showed no treeline ascent.
In causal reasoning, showing that the effect does not occur when the hypothesized cause (hare decline) is absent, even when the rival factor (warming) is present, strongly reinforces the author's causal attribution.
3
Determine the truth value of the evaluated claim.
Because the supplementary finding directly strengthens the ecologist's conclusion by eliminating a rival explanation and demonstrating causation through a negative control, the claim is True.
Aligns the assessed relationship with standard logical reasoning criteria for strengthen tasks.

Key Concept

Causal strengthening via negative control and elimination of rival explanations
Estimated Time:1m 15s
Question 36Question →

Agricultural Economist: In the province of Vallesia, smallholder tomato farmers historically suffered severe post-harvest crop losses due to fungal spoilage during transit. Three years ago, the regional agricultural ministry subsidized the distribution of solar-powered ventilated storage crates. Over the subsequent two years, recorded post-harvest tomato losses across the province fell by nearly 60 percent, leading the ministry to conclude that the crates were responsible for the improvement. However, during the exact same period, an unseasonably severe drought lowered ambient humidity throughout Vallesia's transport corridors. Because ambient fungal spore germination is heavily inhibited in arid conditions, the reduction in tomato spoilage was almost certainly caused by the drought rather than the ventilated crates.

Which of the following, if true, most strengthens the agricultural economist's argument?

Show answer & explanation

Answer: Smallholder tomato farmers in Vallesia who continued using traditional unventilated crates throughout the two-year drought experienced a decrease in fungal spoilage comparable to that reported by farmers using the ventilated crates.

Answer

The argument is most strengthened by demonstrating that tomato farmers who did not use the ventilated crates during the drought still experienced a comparable reduction in spoilage.
The correct answer provides critical comparative evidence: by showing that tomato farmers who never used the ventilated storage crates experienced the exact same reduction in fungal spoilage during the drought period, it isolates the regional aridity as the primary driver of the reduction and confirms that the crates were not necessary to produce the outcome.

Step-by-Step Solution

1
Analyze the stimulus argument structure and identify the main conclusion and competing causal explanations.
Conclusion: The drought, rather than the ventilated crates, caused the 60 percent decline in post-harvest fungal spoilage. Premise: Fungal spore germination is inhibited in arid conditions, and a drought coincided with crate deployment.
Strengthen questions require isolating the author's specific conclusion and determining what assumption or evidence is needed to favor the author's causal claim over the rival hypothesis.
2
Identify the reasoning gap in the causal attribution.
The author assumes that the correlation between the drought and the drop in spoilage reflects a genuine causal relationship, and that the crates did not contribute meaningfully to the reduction.
To strengthen a causal argument ruling out an alternative cause, a strong strategy is to demonstrate that when the alternative cause (the crates) is absent but the favored cause (the drought) is present, the effect (reduced spoilage) still occurs.
3
Evaluate the answer choices to identify the statement that provides this comparative evidentiary support.
The finding that farmers using traditional crates had identical spoilage reductions during the drought isolates the drought as the operative causal factor and rules out the crates.
This establishes a classic control group that directly reinforces the economist's causal conclusion.

Key Concept

Causal strengthening through control-group evidence (effect occurs when alleged cause is absent but candidate cause is present)
Estimated Time:1m 30s
Question 37Question →

Archaeologist: Excavations at the Bronze Age settlement of Tell el-Ajjul revealed a sharp increase in the proportion of ceramic storage jars lined with beeswax starting around 1400 BCE, coinciding with a severe, prolonged regional drought. Because beeswax acts as an effective impermeable sealant against evaporative water loss, researchers concluded that the inhabitants adopted beeswax lining specifically as a technological adaptation to conserve drinking water during the drought.

Statement: The finding that contemporary ceramic storage jars from neighboring settlements that did not experience the drought showed no increase in beeswax lining strengthens the researchers' conclusion.

Show answer & explanation

Answer: True

Answer

True, because establishing that the technological practice did not spread to neighboring drought-free settlements rules out alternative explanations such as general regional trade or cultural diffusion, thereby reinforcing the causal connection to drought adaptation.
The statement accurately identifies a valid strengthening mechanism: providing a control case where the absence of the proposed cause (drought) coincides with the absence of the observed effect (increase in beeswax-lined jars), which effectively rules out broader regional trends.

Step-by-Step Solution

1
Identify the core premises and conclusion of the argument
Premise: Beeswax-lined jars spiked at Tell el-Ajjul during a drought, and beeswax prevents evaporation. Conclusion: The lining was adopted specifically to conserve water in response to that drought.
Isolating the conclusion allows the identification of the underlying causal assumption.
2
Identify the logical vulnerability in the causal attribution
The argument assumes that the increase in beeswax lining was caused by the drought rather than by a general regional innovation, trade shift, or decorative trend unrelated to rainfall.
Strengthening a causal claim often requires demonstrating that the effect does not occur when the proposed cause is absent.
3
Evaluate the impact of the supplementary statement
The statement shows that nearby settlements unaffected by drought did not adopt the practice, providing control evidence that supports the drought-specific cause.
Since the statement supports the causal attribution, the assertion that it strengthens the argument is correct (True).

Key Concept

Strengthening Causal Claims via Control Comparison
Estimated Time:1m 15s
Question 38Question →

Anthropologist: Dental calculus from adult human remains at a 3,500-year-old steppe settlement contains beta-lactoglobulin peptides specifically matching horse milk. Because the equine skeletal remains found at the site lack bit wear on their teeth, some researchers hypothesize that these horses were wild animals hunted solely for game meat rather than managed livestock. However, the presence of equine milk proteins in the adult dental plaque conclusively proves that this community had domesticated horses and was practicing pastoral dairying.

Which of the following, if true, most strengthens the anthropologist's argument?

Show answer & explanation

Answer: The entrapment of detectable concentrations of whey proteins in human dental calculus requires repeated, routine consumption of dairy fluids over many years rather than sporadic ingestion.

Answer

The finding that detectable whey protein entrapment in human dental calculus requires repeated, routine consumption of dairy fluids over many years rather than sporadic ingestion.
The anthropologist infers that the steppe community domesticated horses and practiced dairying from the presence of horse milk whey proteins in adult human dental calculus, rejecting the skeptic's counterhypothesis that the horses were wild game hunted for meat. The underlying vulnerability is that hunters might have occasionally ingested milk from slaughtered wild nursing mares. Establishing that detectable whey protein entrapment in dental plaque requires repeated, long-term dairy consumption over many years rules out sporadic ingestion from hunted wild game, thereby substantially strengthening the conclusion that the population maintained live domestic herds for ongoing dairy exploitation.

Step-by-Step Solution

1
Isolate the argument's core premises and conclusion.
The anthropologist concludes that the community domesticated horses for dairying based on the discovery of equine milk whey proteins in human dental calculus, despite the lack of bit wear on horse teeth.
Clarifying the inferential leap reveals the vulnerability in the author's reasoning.
2
Identify the primary competing hypothesis and underlying assumption.
Skeptics suggest the horses were merely wild game; the anthropologist assumes that finding milk proteins cannot be explained by opportunistically consuming milk from killed wild mares.
To strengthen an argument that attributes physical evidence to a specific behavior, one must rule out alternative mechanisms capable of generating that same evidence.
3
Evaluate the choices to find the statement that eliminates the rival hypothesis.
Demonstrating that whey protein entrapment requires chronic, multi-year dairy ingestion confirms that sporadic consumption from hunted wild carcasses could not have generated the observed dental evidence.
Eliminating the hunting counterexplanation directly supports the conclusion that the horses were managed livestock.

Key Concept

Strengthening an argument by eliminating a competing causal explanation
Question 39Question →

Match each argument with the supplementary premise that most effectively strengthens its central conclusion.

Click a left item, then click its matching right item

Items

Argument 1: Regional transit authorities recorded a 25% decline in suburban commuter rail usage following the completion of a municipal high-speed broadband network, concluding that improved internet connectivity caused residents to adopt telecommuting.
Argument 2: Sleep clinic subjects exposed to rhythmic acoustic pulses during slow-wave sleep demonstrated significantly higher word-pair recall the following morning than unexposed subjects, prompting researchers to conclude that acoustic stimulation during sleep directly strengthens neural memory consolidation.
Argument 3: Archaeologists excavating an ancient port city uncovered charred millet grains in strata dating to an 8th-century BCE arid crisis, leading them to conclude that the settlement's agriculturalists shifted to drought-tolerant millet to adapt to the drying climate.

Matches

Show answer & explanation

Answer

Argument 1 matches the premise confirming increased suburban telecommuting following broadband rollout; Argument 2 matches the premise establishing identical sleep architecture and disturbance levels between cohorts; Argument 3 matches the premise verifying local millet cultivation during the drought era.
Each correct pairing provides crucial evidential support tailored to the specific logical vulnerability of the argument: verifying the causal mechanism for Argument 1, controlling for confounding sleep factors in Argument 2, and eliminating external trade origin in Argument 3.

Step-by-Step Solution

1
Identify the unstated assumption and potential alternative explanations in Argument 1.
Argument 1 assumes that broadband installation actually led to telecommuting rather than rail ridership dropping due to external economic or transit factors.
Strengthening a causal argument requires providing evidence for the hypothesized link or ruling out competing causes.
2
Identify potential confounding variables in Argument 2.
Argument 2 assumes acoustic pulses directly aided consolidation rather than acting as a buffer against ambient awakening or altering sleep stages.
Strengthening an experimental finding involves controlling for confounding variables and confirming equal baseline conditions.
3
Identify alternative origin hypotheses in Argument 3.
Argument 3 assumes the millet found in storage vessels was cultivated locally to cope with drought rather than imported from elsewhere.
Ruling out the trade import alternative directly validates the claim of local agricultural adaptation.

Key Concept

Strengthening Logical Arguments
Estimated Time:1m 30s
Question 40Question →

Marine Biologist: Deep-sea bamboo corals incorporate trace elements from surrounding seawater into their calcite skeletons as they grow. Recent chemical analyses of fossilized bamboo coral specimens collected from the Tasmanian Seamounts revealed that specimens dating to the Younger Dryas cooling period contain significantly higher barium-to-calcium ratios than specimens from adjacent warmer epochs. Because elevated barium concentrations in seawater are primarily associated with the upwelling of nutrient-rich, deep polar waters, researchers concluded that a major northward shift in sub-Antarctic deep ocean currents occurred during the Younger Dryas.

Which of the following, if true, most strengthens the marine biologist's argument?

Show answer & explanation

Answer: Variations in seawater temperature do not significantly alter the ratio at which living bamboo corals incorporate barium relative to calcium from seawater of a given chemical composition.

Answer

The statement establishing that seawater temperature variations do not significantly alter the ratio at which living bamboo corals incorporate barium relative to calcium from seawater of a given chemical composition.
The conclusion asserts that a northward shift of sub-Antarctic polar waters occurred based on higher barium-to-calcium ratios found in corals from a cold period. A major potential flaw is that the cold water temperatures themselves might have caused the corals to absorb more barium regardless of ambient water chemistry. The correct answer eliminates this alternative explanation by confirming that temperature does not alter barium uptake, ensuring the observed ratio reflects actual changes in water composition.

Step-by-Step Solution

1
Analyze the argument's structure, premises, and conclusion.
Premise: Younger Dryas coral fossils have higher barium-to-calcium ratios than corals from warmer epochs. Premise: High seawater barium indicates deep polar water upwelling. Conclusion: A major northward shift in sub-Antarctic deep ocean currents occurred during the Younger Dryas.
Identifying the premises and conclusion clarifies the logical leap between skeletal chemistry and ocean current movement.
2
Identify potential vulnerabilities or unstated assumptions in the reasoning.
The author assumes that the elevated barium-to-calcium ratio in the corals reflects actual higher environmental barium concentrations in the water, rather than a physiological response to the colder temperatures of the Younger Dryas period.
Strengthening questions often require ruling out plausible rival explanations or validating the reliability of a physical proxy.
3
Evaluate the answer choices to identify the statement that best defends the argument against alternative explanations.
The statement confirming that temperature changes do not alter barium uptake ratios eliminates temperature as a confounding cause, thereby strengthening the conclusion that ambient polar water upwelling caused the observed ratio.
Ruling out an alternative hypothesis directly supports the causal attribution made by the researcher.

Key Concept

Ruling out an alternative cause / validating an empirical proxy
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