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Question 1541Question →

Passage Excerpt:
In 1947, while working on the Harvard Mark II computer, computer scientist Grace Hopper and her team encountered a sudden system error. Upon examining the machine's hardware, they discovered a moth trapped in one of the electromagnetic relays. They carefully removed the insect and taped it into their logbook, [underlined portion], to document the unusual breakdown.

The writer wants to edit the underlined portion to emphasize the historic significance of this event as the origin of the computer programming term "debugging." Which choice best accomplishes this goal?

Show answer & explanation

Answer: coining the phrase 'first actual case of bug being found' and inspiring the modern programming term 'debugging'

Answer

coining the phrase 'first actual case of bug being found' and inspiring the modern programming term 'debugging'
The choice that mentions coining the phrase 'first actual case of bug being found' and inspiring the modern programming term 'debugging' is correct because it directly addresses the writer's goal to highlight the origin of the term 'debugging' in computer programming.

Step-by-Step Solution

1
Analyze the prompt to identify the specific rhetorical goal.
The goal is to choose an option that emphasizes the historic significance of the event as the origin of the term 'debugging'.
ACT English questions of this type require satisfying a highly specific prompt constraint.
2
Evaluate the choices for grammatical correctness and relevance to the goal.
Identify that the choice referencing the coining of 'first actual case of bug being found' and 'debugging' is grammatically correct and directly addresses the goal. The other choices either focus on irrelevant details or contain grammatical errors like comma splices.
This process eliminates distractors that are either grammatically incorrect or rhetorically off-topic.
3
Select the correct option based on this evaluation.
The choice mentioning the coining of the phrase and inspiring 'debugging' is selected.
It is the only choice that successfully fulfills the rhetorical goal stated in the prompt.

Key Concept

Meeting Specific Rhetorical Goals
Question 1542Question →

A positive integer nn has exactly two distinct prime factors, pp and qq, such that p+q=12p + q = 12. If nn has exactly 8 positive factors, what is the least possible value of nn?

Show answer & explanation

Answer: 875

Answer

875
The prime factors of the number must be 5 and 7 since they are the only prime numbers that sum to 12. For a number with prime factorization 5a×7b5^a \times 7^b, the number of factors is (a+1)(b+1)=8(a+1)(b+1) = 8. Since both prime factors must be present, the exponents must be 1 and 3. The two possible numbers are 53×71=8755^3 \times 7^1 = 875 and 51×73=1,7155^1 \times 7^3 = 1,715. The least value is 875.

Step-by-Step Solution

1
Find the two prime numbers pp and qq that sum to 12.
The prime factors are 5 and 7.
Since pp and qq are prime and p+q=12p + q = 12, we test pairs of positive integers. The only pair of prime numbers that sums to 12 is 5 and 7.
2
Express the number of factors of nn using the prime factorization formula.
The number of factors is (a+1)(b+1)=8(a + 1)(b + 1) = 8.
For any positive integer n=pa×qbn = p^a \times q^b, the number of positive factors is given by the formula (a+1)(b+1)(a + 1)(b + 1).
3
Determine the possible values for the exponents aa and bb.
The set of exponents {a,b}\{a, b\} must be {1,3}\{1, 3\}.
Since nn must contain both prime factors, a≥1a \ge 1 and b≥1b \ge 1, which means (a+1)≥2(a + 1) \ge 2 and (b+1)≥2(b + 1) \ge 2. The only factor pair of 8 where both factors are at least 2 is 2×42 \times 4. Thus, one exponent must be 1 and the other must be 3.
4
Calculate the possible values of nn and identify the least value.
The least value is 875.
The two possible values for nn are 53×71=125×7=8755^3 \times 7^1 = 125 \times 7 = 875 and 51×73=5×343=1,7155^1 \times 7^3 = 5 \times 343 = 1,715. The least possible value is 875.

Key Concept

Factors, Multiples, and Prime Factorization
Question 1543Question →

Read the passage and answer the question that follows.

[1] In 1952, computer scientist Grace Hopper developed the A-0 System, which is widely considered the first compiler. [2] Before this breakthrough, programmers had to write code in tedious machine language, consisting entirely of binary numbers. [3] Hopper proposed a system that would allow programmers to write instructions in English-like statements, which the compiler would then translate into machine code. [4] Many of her contemporaries, however, doubted this was possible, believing that computers were only capable of understanding arithmetic. [5] Hopper’s favorite hobby, needlepoint, required a similar kind of meticulous, pattern-based thinking. [6] Despite this skepticism, Hopper persisted, and her work eventually laid the foundation for modern programming languages like COBOL.

The writer is considering deleting Sentence 5 from the passage. Should the sentence be kept or deleted?

Show answer & explanation

Answer: Deleted, because it interrupts the discussion of Hopper's work on compilers with an irrelevant detail about her personal hobby.

Answer

The sentence should be deleted because it interrupts the discussion of Hopper's work on compilers with an irrelevant detail about her personal hobby.
The correct choice is to delete the sentence because it introduces a personal detail about Grace Hopper's hobby (needlepoint) that is irrelevant to the technical and historical focus of the paragraph. Deleting it maintains the paragraph's unity and smooth transition from Sentence 4 to Sentence 6.

Step-by-Step Solution

1
Identify the main topic and focus of the paragraph.
The paragraph centers on Grace Hopper's creation of the A-0 compiler system and the skepticism she overcame from her contemporaries.
Understanding the paragraph's primary focus is essential for evaluating whether a sentence is relevant to its cohesion and unity.
2
Analyze the content and purpose of Sentence 5.
Sentence 5 introduces biographical details about Hopper's hobby (needlepoint) and draws a parallel to pattern-based thinking.
Analyzing the proposed sentence helps determine if it adds value or diverts the reader's attention.
3
Evaluate the flow and logical connection between the sentences surrounding Sentence 5.
Sentence 4 describes the skepticism of her peers, and Sentence 6 describes how Hopper persisted despite this skepticism. Sentence 5 interrupts this direct cause-and-effect relationship with unrelated personal information.
Assessing flow shows whether the sentence acts as a transition or a distraction.

Key Concept

Sentence Addition and Deletion Decisions
Question 1544Question →

What is the least common multiple of 1515 and 2020?

Show answer & explanation

Answer: 60

Answer

The least common multiple of 1515 and 2020 is 6060.
The correct answer is 6060. The least common multiple is the smallest positive integer that is divisible by both 1515 and 2020. By listing multiples or using prime factorization (22×3×52^2 \times 3 \times 5), we arrive at 6060.

Step-by-Step Solution

1
Find the prime factorization of 1515 and 2020.
15=3×515 = 3 \times 5 and 20=22×520 = 2^2 \times 5.
Decomposing numbers into their prime factors makes it straightforward to compute their least common multiple.
2
Identify the highest exponent for each prime factor appearing in the prime factorizations.
The prime factors present are 22, 33, and 55. The highest powers are 222^2, 313^1, and 515^1.
The least common multiple must contain all prime factors of both numbers at their maximum frequency to be divisible by both.
3
Calculate the product of these highest powers of the prime factors.
22×3×5=4×3×5=602^2 \times 3 \times 5 = 4 \times 3 \times 5 = 60.
Multiplying these factors yields the smallest positive integer that is a multiple of both original numbers.

Key Concept

Least Common Multiple (LCM)
Estimated Time:45s
Question 1545Question →

Two cyclists, Alan and Beatrice, begin riding laps around a circular track at the same time, starting from the same line and traveling in the same direction. Alan completes one lap every 40 seconds, and Beatrice completes one lap every 50 seconds. What is the number of laps Beatrice will have completed the next time they both cross the starting line at the same instant?

Show answer & explanation

Answer: 4

Answer

Beatrice will have completed 4 laps.
The correct answer is 4. The two cyclists will meet at the starting line after a period of time that is a multiple of both of their lap times. The first time they meet after starting is the least common multiple (LCM) of 40 and 50, which is 200 seconds. Dividing the total time of 200 seconds by Beatrice's lap time of 50 seconds yields 4 laps.

Step-by-Step Solution

1
Find the prime factorizations of both lap times to determine their least common multiple (LCM).
The prime factorization of 40 is 23×512^3 \times 5^1, and the prime factorization of 50 is 21×522^1 \times 5^2.
They will cross the starting line together at times that are common multiples of their individual lap times.
2
Calculate the LCM by taking the highest power of each prime factor present in either factorization.
LCM(40,50)=23×52=8×25=200\text{LCM}(40, 50) = 2^3 \times 5^2 = 8 \times 25 = 200 seconds.
The least common multiple represents the minimum amount of time that must pass before both cyclists reach the starting line at the same time.
3
Divide the total time elapsed by Beatrice's time per lap to find the number of laps she completes.
200 seconds÷50 seconds per lap=4200 \text{ seconds} \div 50 \text{ seconds per lap} = 4 laps.
This converts the total time until they meet into the number of laps completed specifically by Beatrice.

Key Concept

Least Common Multiple (LCM) and rate calculations
Estimated Time:1m 0s
Question 1546Question →

If the mathematical expression below is simplified using the standard order of operations, what is the result?

12−6÷2×3+42 12 - 6 \div 2 \times 3 + 4^2
Show answer & explanation

Answer: 19

Answer

The correct result of the expression is 19.
The correct value is obtained by first evaluating the exponent (42=164^2 = 16), then performing the division and multiplication from left to right (6÷2=36 \div 2 = 3, followed by 3×3=93 \times 3 = 9), and finally performing the subtraction and addition from left to right (12−9=312 - 9 = 3, followed by 3+16=193 + 16 = 19).

Step-by-Step Solution

1
Evaluate the exponent term.
42=164^2 = 16
Exponents must be evaluated before multiplication, division, addition, and subtraction.
2
Perform multiplication and division from left to right.
6÷2×3=3×3=96 \div 2 \times 3 = 3 \times 3 = 9
Multiplication and division have equal precedence, so they are processed in order from left to right.
3
Perform addition and subtraction from left to right.
12−9+16=3+16=1912 - 9 + 16 = 3 + 16 = 19
Addition and subtraction have equal precedence, so they are processed in order from left to right.

Key Concept

Order of Operations (PEMDAS)
Question 1547Question →

For all real numbers aa and bb, which of the following expressions is equivalent to a−b[a−(b−a)]−b2a - b[a - (b - a)] - b^2?

Show answer & explanation

Answer: a−2aba - 2ab

Answer

The expression a−2aba - 2ab
To simplify the expression, we begin inside the innermost grouping symbols (the parentheses) and work outward. First, we distribute the negative sign to simplify the term inside the brackets: a−(b−a)=a−b+a=2a−ba - (b - a) = a - b + a = 2a - b. Next, we distribute the −b-b term outside the brackets to get −b(2a−b)=−2ab+b2-b(2a - b) = -2ab + b^2. Substituting this back into the main expression gives a−2ab+b2−b2a - 2ab + b^2 - b^2. Combining the like terms b2−b2=0b^2 - b^2 = 0 simplifies the expression to a−2aba - 2ab.

Step-by-Step Solution

1
Simplify the expression inside the brackets by distributing the negative sign across the parentheses.
a−(b−a)=a−b+a=2a−ba - (b - a) = a - b + a = 2a - b
According to the order of operations, terms inside parentheses must be simplified first.
2
Substitute the simplified bracket expression back into the main expression.
a−b[2a−b]−b2a - b[2a - b] - b^2
This sets up the expression for the next operation, which is multiplication.
3
Distribute the term −b-b across the bracketed expression.
−b(2a−b)=−2ab+b2-b(2a - b) = -2ab + b^2
Multiplication must be performed before subtraction. Multiplying two negative signs yields a positive term.
4
Combine the distributed terms back into the full expression and simplify like terms.
a−2ab+b2−b2=a−2aba - 2ab + b^2 - b^2 = a - 2ab
Combining the positive and negative b2b^2 terms results in 00, leaving the fully simplified expression.

Key Concept

Order of Operations and Number Properties

Alternative Method

Instead of simplifying algebraically, you can substitute simple numbers for aa and bb. Let a=2a = 2 and b=3b = 3. Evaluating the original expression: 2−3[2−(3−2)]−32=2−3[2−1]−9=2−3(1)−9=−102 - 3[2 - (3 - 2)] - 3^2 = 2 - 3[2 - 1] - 9 = 2 - 3(1) - 9 = -10. Substituting a=2a = 2 and b=3b = 3 into the correct option a−2aba - 2ab gives 2−2(2)(3)=2−12=−102 - 2(2)(3) = 2 - 12 = -10. This numerical substitution confirms the correct algebraic simplification.
Estimated Time:1m 30s
Question 1548Question →

A writer is editing a passage about the preservation of the Tudor warship Mary Rose.

In 1982, the hull of the Tudor warship Mary Rose was raised from the Solent seabed, where it had rested since sinking in 1545. Once retrieved, the waterlogged timbers faced the immediate threat of rapid drying and decay. To prevent this, conservators sprayed the hull continuously with cold freshwater, followed by a mist of polyethylene glycol (PEG), a water-soluble wax that gradually replaced the water in the wood cells. [1] This painstaking process took decades, concluding only in 2013 when the ship was finally allowed to dry under controlled conditions. Today, the ship is housed in a museum in Portsmouth, attracting thousands of visitors annually.

The writer is considering adding the following sentence to the paragraph at Point [1]:

"Polyethylene glycol is also commonly used as an additive in cosmetics, toothpastes, and various pharmaceutical products."

Should the writer make this addition?

Show answer & explanation

Answer: No, because it interrupts the paragraph's description of the ship's conservation process with details that are irrelevant to the topic.

Answer

The correct option is the one stating that the addition should not be made because it interrupts the paragraph's description of the ship's conservation process with details that are irrelevant to the topic.
The correct option is the one stating that the addition should not be made because it interrupts the paragraph's description of the ship's conservation process with details that are irrelevant to the topic. The paragraph focus is strictly on the history, recovery, and conservation of the Mary Rose. Introducing everyday applications of polyethylene glycol deviates from this focus, making the sentence irrelevant.

Step-by-Step Solution

1
Analyze the main focus of the paragraph.
The paragraph describes the retrieval and conservation process of the Tudor warship Mary Rose, specifically detailing how conservators prevented the waterlogged wood from decaying using water and polyethylene glycol (PEG).
To evaluate whether the proposed sentence is relevant, we must first establish the specific topic of the paragraph.
2
Analyze the proposed sentence to see if it supports or expands upon this main focus.
The proposed sentence discusses other common uses of polyethylene glycol (PEG) in cosmetics, toothpaste, and pharmaceuticals.
Determining the function of the new sentence helps identify if it adds valuable information or creates a digression.
3
Compare the purpose of the sentence with the paragraph focus to determine if it should be added.
The proposed sentence introduces details about everyday consumer products that are completely unrelated to ship conservation, meaning it disrupts the logical flow and should not be added.
Rhetorical relevance requires every sentence in a paragraph to support the paragraph's central point.

Key Concept

Evaluating the relevance of adding information to a paragraph based on its main focus and unity.
Question 1549Question →

In 1977, researchers aboard the research submersible *Alvin* made a startling discovery on the ocean floor: hydrothermal vents teeming with life. Prior to the time when this discovery was made by the researchers, scientists believed that all life on Earth ultimately depended on sunlight for energy.

Which of the following is the best revision of the underlined portion of the sentence?

Show answer & explanation

Answer: Before this discovery,

Answer

Before this discovery,
The correct option is the most concise and direct phrasing that maintains grammatical correctness and correctly introduces the clause.

Step-by-Step Solution

1
Analyze the underlined portion for conciseness, clarity, and voice.
The original phrase is wordy and uses an inactive, passive construction ('was made by the researchers') to express a simple chronological relationship.
ACT English questions prioritize economy of language and active voice.
2
Evaluate the grammar and meaning of the remaining choices.
One option introduces a subordinating conjunction that turns the sentence into a fragment, another creates a comma splice, and the remaining option is concise and grammatically correct.
Eliminating options that introduce new grammatical errors reveals the correct answer.

Key Concept

Eliminating Wordiness
Estimated Time:1m 0s
Question 1550Question →

Unlike other ancient pigments that fade over centuries, Maya Blue has remained remarkably vibrant. This durability stems from a unique chemical synergy: the indigo dye molecule becomes encapsulated within the clay channels of palygorskite. Researchers who analyzed the pigment's thermal stability concluded that the bonding process makes the pigment super tough when it faces intense heat or acid exposure.

Which choice most effectively maintains the established tone of the passage?

Show answer & explanation

Answer: renders the pigment highly resilient to

Answer

The phrasing 'renders the pigment highly resilient to' most effectively maintains the established academic tone and uses correct idiomatic preposition usage.
The correct choice maintains the academic register of the passage by using 'renders the pigment highly resilient to,' which aligns with the scientific vocabulary of the context and utilizes the correct idiomatic preposition.

Step-by-Step Solution

1
Analyze the tone of the surrounding sentences in the passage.
The passage uses formal, precise scientific terminology such as 'durability,' 'chemical synergy,' 'encapsulated,' and 'thermal stability,' establishing an academic tone.
Identifying the register of the text ensures the selected option is stylistically consistent.
2
Evaluate the choices to eliminate options that violate this established tone.
The original phrasing 'makes the pigment super tough' is too colloquial. The phrasing 'begets an era of absolute invulnerability' is overly dramatic and wordy. The phrase 'renders the pigment highly resilient' matches the objective, formal tone.
Filtering options by stylistic appropriateness narrows down the candidates.
3
Compare the remaining choices for grammatical correctness and idiomatic usage.
The adjective 'resilient' idiomatically requires the preposition 'to' rather than 'from' when describing resistance to external forces like heat or acid. Therefore, 'resilient to' is the correct formulation.
Ensuring the choice complies with standard conventions of English usage.

Key Concept

Tone Consistency
Estimated Time:1m 0s
Question 1551Question →

Passage

Modern airports employ a variety of high-tech methods to prevent bird strikes, which can cause catastrophic engine failure during takeoff. Automated radar systems scan the skies, and sound cannons emit loud blasts to scare away flocks[1] . Consequently, many facility managers have found that these mechanical solutions are less effective over time as birds become habituated to the noise. Instead, airports are increasingly turning to falconry, using trained birds of prey to naturally deter other avian species from nesting near runways.

Which choice provides the most logical and grammatically correct transition between the two sentences?

Show answer & explanation

Answer: . However,

Answer

The correct option is the one that uses a period followed by the contrasting transition '. However,'.
The correct answer is the option that presents '. However,'. The relationship between the first sentence (describing active bird mitigation efforts) and the second sentence (describing their eventual failure due to habituation) is contrasting. Thus, a contrast transition is needed. Grammatically, because both clauses are independent, they must be separated by a period, making this punctuation and word choice correct.

Step-by-Step Solution

1
Analyze the logical relationship between the sentence about using radar and sound cannons and the sentence about managers finding these solutions less effective.
The second sentence presents a limitation or drawback to the first sentence, indicating a relationship of contrast rather than cause-and-effect or addition.
Identifying the correct relationship allows us to eliminate transition words that convey the wrong logic.
2
Determine the grammatical structure of both clauses.
Both clauses ('Automated radar systems scan the skies...' and 'many facility managers have found...') are independent clauses that can stand alone as sentences.
Understanding the clause type ensures we apply proper punctuation rules to avoid sentence structure errors like comma splices.
3
Evaluate the choices for both logical fit and grammatical correctness.
The option '. However,' provides the appropriate contrast transition and properly separates the two independent clauses with a period.
This step ensures the chosen answer is both contextually logical and grammatically precise.

Key Concept

Selecting appropriate transition words based on the logical relationship between sentences and ensuring proper punctuation is used when joining independent clauses.
Estimated Time:1m 0s
Question 1552Question →

What is the value of the mathematical expression below?

−32+4×[18−3×(8−4)]÷2 -3^2 + 4 \times [18 - 3 \times (8 - 4)] \div 2
Show answer & explanation

Answer: 3

Answer

The correct value of the expression is 3.
Following the standard order of operations, we first simplify the nested parentheses (8−4)=4(8 - 4) = 4. Next, we evaluate the expression inside the brackets [18−3×4]=[18−12]=6[18 - 3 \times 4] = [18 - 12] = 6. We then evaluate the exponent −32=−9-3^2 = -9. We perform the multiplication and division from left to right: 4×6÷2=124 \times 6 \div 2 = 12. Finally, adding −9+12-9 + 12 yields the correct result of 3.

Step-by-Step Solution

1
Simplify the innermost parentheses.
−32+4×[18−3×4]÷2-3^2 + 4 \times [18 - 3 \times 4] \div 2
According to the order of operations (PEMDAS), operations inside parentheses or grouping symbols must be performed first.
2
Simplify the expression inside the square brackets by performing multiplication before subtraction.
−32+4×6÷2-3^2 + 4 \times 6 \div 2
Multiplication has a higher precedence than subtraction.
3
Evaluate the exponent −32-3^2.
−9+4×6÷2-9 + 4 \times 6 \div 2
The exponent applies only to the base 3, not to the negative sign, because there are no parentheses around −3-3.
4
Perform multiplication and division from left to right.
−9+12-9 + 12
Multiplication and division have the same precedence and must be evaluated in order from left to right.
5
Add the remaining values.
33
Addition is the final operation to perform.

Key Concept

Order of operations (PEMDAS) dictates the sequence in which operations must be performed to evaluate an expression: Parentheses/Brackets, Exponents, Multiplication and Division (from left to right), and Addition and Subtraction (from left to right).
Question 1553Question →

[1] When chief engineer Washington Roebling became bedridden with decompression sickness during the construction of the Brooklyn Bridge, the project faced a crisis. [2] Fortunately, his wife, Emily Warren Roebling, stepped in to serve as his liaison, translating his instructions for the construction crew. [3] She studied advanced mathematics, materials science, and bridge engineering to prepare herself for this daunting task. [4] Over the next decade, she took over much of the day-to-day supervision of the site, earning the deep respect of both the workers and the trustees. [5] By the time the bridge opened in 1883, she was widely recognized as the driving force behind its completion.

For the sake of logic and cohesion, the writer wants to add the following sentence to the paragraph:

"To perform this role effectively, she had to master complex technical concepts that were typically closed to nineteenth-century women."

To make the paragraph most logical, where should this sentence be placed?

Show answer & explanation

Answer: after Sentence 2

Answer

after Sentence 2
The correct answer is the option that places the sentence after Sentence 2. The demonstrative pronoun phrase "this role" refers directly to the role of "liaison" established in Sentence 2. Furthermore, mentioning the need to "master complex technical concepts" provides a logical transition into Sentence 3, which details the specific subjects Emily studied to achieve that mastery.

Step-by-Step Solution

1
Identify the logical indicators and pronouns in the sentence to be inserted.
The phrase "this role" requires a previously mentioned role, and the concept of mastering "complex technical concepts" needs to connect to specific technical subjects.
Tracking pronouns and key concepts helps establish the required context preceding and following the target sentence.
2
Locate the introduction of the role referenced by the pronoun.
Sentence 2 introduces Emily Warren Roebling's role as a "liaison" who translated technical instructions.
This establishes that the target sentence must come after Sentence 2.
3
Connect the requirement of mastering technical concepts to the subsequent actions described in the paragraph.
Sentence 3 describes Emily studying advanced mathematics, materials science, and bridge engineering, which represents the execution of mastering those concepts.
This shows that the target sentence must precede Sentence 3, pointing to the location after Sentence 2.

Key Concept

Sentence Reordering and Placement
Question 1554Question →

What is the value of the expression ∣−12∣−∣7−15∣|-12| - |7 - 15|?

Show answer & explanation

Answer: 4

Answer

The value of the expression is 4.
The absolute value of a number represents its distance from zero on a number line, so ∣−12∣=12|-12| = 12. Simplifying inside the second term gives 7−15=−87 - 15 = -8, and the absolute value ∣−8∣=8|-8| = 8. Subtracting these two results yields 12−8=412 - 8 = 4.

Step-by-Step Solution

1
Evaluate the first term
∣−12∣=12|-12| = 12
The absolute value of a number is its distance from zero on the number line, which is always non-negative.
2
Simplify the expression inside the second absolute value
7−15=−87 - 15 = -8
Subtracting 15 from 7 yields a negative difference of -8.
3
Evaluate the second absolute value term
∣−8∣=8|-8| = 8
The absolute value of -8 is 8.
4
Subtract the two evaluated terms
12−8=412 - 8 = 4
Subtracting 8 from 12 gives the final simplified value of 4.

Key Concept

Evaluating expressions with absolute values requires simplifying the terms inside the absolute value grouping symbols first, taking the absolute value of the result, and then performing the subtraction.
Question 1555Question →

At the Harvard College Observatory in the early twentieth century, Henrietta Swan Leavitt analyzed photographic glass plates to catalog the brightness of stars. By comparing plates taken at different times, she noticed a pattern in a class of pulsating stars known as Cepheid variables: the brighter stars took longer to cycle through their periods of light variation. This relationship allowed astronomers to calculate cosmic distances, which [exploded] our understanding of the scale of the universe. In an era when women were largely restricted from operating telescopes, Leavitt's meticulous calculations laid the foundation for modern cosmology.

Which choice most precisely and clearly completes the sentence while maintaining the passage's formal, academic tone?

Show answer & explanation

Answer: expanded

Answer

expanded
The correct option is 'expanded' because it precisely and clearly describes the widening of astronomical knowledge using a tone that is consistent with the academic and objective style of the passage.

Step-by-Step Solution

1
Analyze the context of the sentence and the established tone of the passage.
The passage describes Henrietta Swan Leavitt's monumental scientific discovery in a formal, objective, and academic tone.
Understanding the context and register helps eliminate choices that are too informal or stylistically inappropriate.
2
Evaluate the underlined word 'exploded' for tone and precision.
While 'exploded' metaphorically conveys a massive change, its register is too colloquial and dramatic for a scientific history narrative.
This identifies the need to replace the original wording.
3
Assess the remaining options ('expanded', 'escalated', 'dilated') for semantic precision and correctness.
'Escalated' incorrectly implies a rising conflict or tension, while 'dilated' refers only to physical widening. 'Expanded' fits both the semantic meaning of broadening intellectual scope and the academic tone.
This narrows down the choices to the single correct option.

Key Concept

Selecting words that precisely fit the context and maintain a consistent tone
Question 1556Question →

A writer is editing a passage about the history of the neon sign and has drafted the following paragraph:

In 1910, French engineer Georges Claude introduced the first neon lamp to the public at the Paris Motor Show. Claude had discovered that passing an electrical current through sealed glass tubes containing neon gas produced a bright, glowing red light. [1] Seeking to commercialize his invention, Claude founded a company called Claude Neon to sell these vibrant tubes for advertising. By the 1920s, neon signs had crossed the Atlantic, transforming the nightscapes of American cities like Los Angeles and New York with their electric glow.

At Point [1], the writer is considering adding the following sentence:
"Neon is a noble gas, which means it is colorless, odorless, and highly unreactive under normal conditions."

Should the writer make this addition?

Show answer & explanation

Answer: No, because it interrupts the paragraph's focus on the development and commercialization of the neon lamp with irrelevant chemical details.

Answer

No, because it interrupts the paragraph's focus on the development and commercialization of the neon lamp with irrelevant chemical details.
The correct option correctly identifies that the proposed sentence should not be added because it introduces irrelevant chemical facts about neon gas that disrupt the paragraph's narrative focus on the commercial history and development of the neon lamp.

Step-by-Step Solution

1
Analyze the main focus of the paragraph.
The paragraph focuses on the historical introduction of the neon lamp by Georges Claude and its commercial expansion.
Understanding the paragraph's core topic helps determine whether new details are relevant.
2
Evaluate the relevance of the proposed sentence.
The proposed sentence discusses the general chemical properties of neon as a noble gas.
Determining if the proposed sentence supports the established focus or deviates from it.
3
Decide whether to add the sentence and select the correct justification.
The sentence should not be added because chemical properties of the gas are irrelevant to the historical and commercial narrative of the neon sign.
Eliminating options that suggest adding the sentence or offer incorrect reasons for deleting it.

Key Concept

Evaluating Relevance for Adding or Deleting Content
Estimated Time:1m 0s
Question 1557Question →

[1] For centuries, scientists have marveled at the durability of ancient Roman concrete, which has survived for two millennia in harsh marine environments. [2] In contrast, modern concrete structures often begin to degrade within a few decades. [3] Recently, researchers discovered that the secret to this longevity lies in 'lime clasts'—small, white mineral chunks found throughout the ancient material. [4] The researchers used high-resolution electron microscopes to analyze the samples in their campus laboratories. [5] Previously dismissed as evidence of poor mixing, these clasts actually provide a self-healing mechanism when water enters cracks in the concrete, reacting to block further damage.

The writer is considering deleting Sentence 4 from the passage. Should this sentence be kept or deleted?

Show answer & explanation

Answer: Deleted, because it interrupts the explanation of the concrete's durability with irrelevant details about laboratory equipment.

Answer

Deleted, because it interrupts the explanation of the concrete's durability with irrelevant details about laboratory equipment.
The correct answer is the option stating that the sentence should be deleted because it interrupts the explanation of the concrete's durability with irrelevant details about laboratory equipment. The paragraph explains why ancient Roman concrete is highly durable, specifically highlighting the recent discovery of 'lime clasts' and how they provide a self-healing mechanism. Sentence 4 introduces tangential information about the specific laboratory equipment (high-resolution electron microscopes) and location of the study, which interrupts the logical explanation of the concrete's chemistry.

Step-by-Step Solution

1
Identify the primary topic and focus of the paragraph.
The paragraph explains why ancient Roman concrete is highly durable, specifically highlighting the recent discovery of 'lime clasts' and how they provide a self-healing mechanism.
Understanding the core topic is necessary to evaluate whether Sentence 4 is relevant or disruptive to the flow.
2
Analyze the content of Sentence 4.
Sentence 4 mentions that researchers used high-resolution electron microscopes in their laboratories to analyze concrete samples.
Evaluating the proposed sentence determines whether it directly supports the paragraph's focus or introduces tangential information.
3
Evaluate the relevance of Sentence 4 and choose the best option.
Since details about laboratory microscopes are irrelevant to the chemical self-healing mechanism of Roman concrete, the sentence should be deleted because it interrupts the explanation of the concrete's durability.
Comparing the sentence's function to the paragraph's purpose reveals that deleting it maintains cohesion and focus.

Key Concept

Sentence Addition and Deletion Decisions
Question 1558Question →

Read the following passage:

During the Klondike Gold Rush, thousands of prospectors traveled to the Yukon Territory [1] in search for fortune, despite the freezing temperatures and treacherous mountain passes.

Which of the following is the best replacement for the underlined portion marked [1]?

Show answer & explanation

Answer: in search of

Answer

in search of
The correct answer is 'in search of' because it is the standard English idiomatic construction used to express that someone is looking for something. When 'search' functions as a noun within this prepositional phrase, it must be paired with the preposition 'of'.

Step-by-Step Solution

1
Analyze the underlined portion 'in search for' and determine if the preposition pairs correctly with the noun 'search' in this specific phrase.
The text uses 'in search for' to show the goal of the prospectors.
Determining idiomatic correctness requires identifying the correct preposition that pairs with 'in search'.
2
Distinguish between the verb form and the noun form of the word 'search' to select the appropriate preposition.
The verb 'search' takes the preposition 'for' (e.g., 'to search for gold'), but the noun in the prepositional phrase 'in search' requires 'of' (e.g., 'in search of gold'). Therefore, the correct option is 'in search of'.
This step resolves the common confusion between the verb and noun forms, allowing the student to select the correct idiom.

Key Concept

Idiomatic preposition usage after nouns
Question 1559Question →

Read the following passage segment:

The vibrant yellow plumage is characteristic with the male American goldfinch during the spring and summer breeding seasons.

Which choice is the most appropriate replacement for the underlined portion?

Show answer & explanation

Answer: characteristic of

Answer

characteristic of
The adjective 'characteristic' is idiomatically followed by the preposition 'of' when defining a trait typical of a specific animal, person, or object. Therefore, the phrase 'characteristic of' correctly connects the plumage to the goldfinch.

Step-by-Step Solution

1
Identify the adjective in the underlined phrase that dictates the correct preposition.
The adjective 'characteristic' must be linked to 'the male American goldfinch.'
English adjectives often require specific prepositions to form standard idiomatic expressions.
2
Determine which preposition standardly pairs with 'characteristic' to indicate a typical feature of a group or species.
The correct idiomatic preposition is 'of,' forming the phrase 'characteristic of.'
Using 'with,' 'to,' or 'for' with 'characteristic' creates an unidiomatic combination that is incorrect in standard written English.

Key Concept

Idiomatic Preposition Usage
Estimated Time:45s
Question 1560Question →

The following passage contains an underlined portion:

To map the ocean floor, scientists use sonar technology to send sound waves into the deep water, and this technique determines the exact, precise location of underwater features.

Which of the following choices best eliminates the redundancy in the underlined portion?

Show answer & explanation

Answer: water, detecting the location

Answer

The correct option is the one that replaces the underlined text with a comma followed by 'detecting the location'. This choice successfully eliminates the synonym redundancy of 'exact' and 'precise' while maintaining correct sentence structure.
The correct option removes the wordy and redundant repetition of synonyms ('exact' and 'precise'). It uses a participial phrase starting with 'detecting' to modify the main clause, which is grammatically correct and concise.

Step-by-Step Solution

1
Identify redundancy in the underlined segment.
The words 'exact' and 'precise' mean the same thing in this context, so one of them must be removed to avoid wordiness.
ACT English questions require eliminating redundant synonym pairs that repeat the same meaning within a sentence.
2
Evaluate the remaining options for grammatical correctness.
The choice ending with 'this determines the location' creates a comma splice. The choice ending with 'Because it determines the location' creates a sentence fragment because it isolates a dependent clause.
An option that eliminates redundancy must not introduce other grammatical errors such as comma splices or fragments.
3
Choose the option that is both grammatically correct and free of redundancy.
The phrase using a participial modifier ('detecting the location') avoids both the redundancy and the grammatical errors, smoothly joining the description to the main clause.
A participial phrase functions as an adjective modifier, avoiding independent clause run-ons or dependent clause fragments.

Key Concept

Eliminating Redundancy
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