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Question

Difficulty: HardStrengthen

The following arguments each rely on unstated assumptions to establish a causal conclusion. Match each argument with the evidentiary finding that most effectively strengthens its central conclusion.

  • An ecologist argues that a mid-sixth-century drought caused a documented spike in catastrophic wildfires, relying on tree-ring data showing low precipitation and concurrent sediment charcoal deposits.Regional estuarine sediment records near continuous human settlements show elevated charcoal deposition only during the specific decades marked by the drought.
  • A behavioral economist concludes that symbolic achievement motives alone drove an 18% shift to off-peak subway travel, based on a trial using an app with digital badges and milestone points but no monetary incentives.Commuters provided with an identical scheduling app that delivered real-time congestion information but lacked badges and milestone points showed no shift in their travel times.
  • A botanist argues that betalain pigment accumulation in desert succulents functions primarily as a physiological shield against ultraviolet radiation damage, noting that pigments only form under intense UV exposure.Mutant succulent specimens unable to synthesize betalain suffer catastrophic cellular DNA degradation when exposed to UV radiation, even under non-dehydrating conditions.

Answer

Match the ecologist's wildfire argument with the estuarine sediment finding showing charcoal spikes restricted to drought decades; match the behavioral economist's transit argument with the control trial showing no shift from an information-only app; and match the botanist's pigment argument with the mutant succulent finding showing cellular DNA damage in the absence of betalain.
Each correct match directly resolves the unique causal vulnerability of the paired argument. The ecologist's argument is strengthened by estuarine data that rules out continuous anthropogenic fire as a confounding factor; the transit study is strengthened by a control group showing information alone was insufficient without gamification; and the botanical claim is strengthened by demonstrating that eliminating the pigment results in UV-induced DNA damage.

Step-by-Step Solution

1
Analyze the reasoning structure and identify the central vulnerability in the ecologist's wildfire argument.
The ecologist infers that drought caused ancient wildfires based solely on temporal coincidence, leaving open the possibility that human land management or independent fire sources caused the charcoal spikes.
Strengthening a causal conclusion requires ruling out alternative explanations or demonstrating consistent covariation between the purported cause and the effect.
2
Analyze the reasoning structure and identify the central vulnerability in the behavioral economist's transit argument.
The economist assumes that symbolic gamification caused the off-peak shift, failing to control for whether the app's underlying scheduling and timing information was the true factor enabling the commuters to reschedule.
A valid strengthener must isolate the causal variable by demonstrating that the effect disappears when the gamification incentive is removed while other features remain constant.
3
Analyze the reasoning structure and identify the central vulnerability in the botanist's pigment argument.
The botanist infers that betalain acts as a protective UV shield because it appears under UV exposure, leaving open whether the pigment is merely an unprotective stress byproduct.
Strengthening requires establishing a direct functional mechanism linking the absence of the substance to the specific physiological harm it is hypothesized to prevent.
4
Match each argument to the finding that directly resolves its specific logical gap.
The wildfire argument matches the estuarine sediment data (ruling out non-drought human burning), the transit argument matches the information-only control group (isolating the badge incentives), and the succulent argument matches the DNA degradation in mutant strains (confirming the protective mechanism of betalain).
Each correct pairing provides the targeted empirical support needed to substantiate the specific unstated causal assumption.

Key Concept

Identifying unstated causal assumptions and pairing them with evidentiary findings that eliminate alternative explanations or isolate causal variables.
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Strengthen

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