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Difficulty: Very hardSelecting Concluding Sentences and Transitions

The following passage is an excerpt from an essay about deep-sea exploration.

In 1977, oceanographers aboard the research vessel *Alvin* descended into the Pacific Ocean near the Galápagos Islands, expecting to find nothing more than a barren, frozen seafloor. To their astonishment, they discovered hydrothermal vents—fissures in the Earth's crust spewing superheated, mineral-rich water. Surrounding these vents were thriving ecosystems teeming with giant tube worms, blind crabs, and ghost-white fish. This discovery revolutionized biology, showing that life could flourish in the complete absence of sunlight by relying on chemosynthesis, a process in which microbes convert toxic chemicals into energy. [1]

The writer wants to add a concluding sentence at point [1] that summarizes the main idea of the paragraph and reinforces the revolutionary impact of the discovery on scientific understanding. Which choice best accomplishes this goal?

  1. A
    The *Alvin* expedition cost millions of dollars, but the crew members were celebrated worldwide for their bravery and findings.
  2. B
    These deep-sea systems rewrote the rules of biology, scientists now had to rethink where life could exist.
  3. Ultimately, the existence of these chemosynthetic communities shattered the long-held scientific consensus that all life on Earth depends on solar energy.Answer
  4. D
    Consequently, the oceanographers who participated in the *Alvin* expedition discover that life could thrive in extreme conditions, which revolutionized modern biology.

Answer

Ultimately, the existence of these chemosynthetic communities shattered the long-held scientific consensus that all life on Earth depends on solar energy.
The correct option summarizes the revolutionary biological impact of the hydrothermal vent discovery by highlighting how it overturned the scientific belief that all life relies on solar energy.

Step-by-Step Solution

1
Analyze the paragraph's main theme and determine the logical goal of the concluding sentence.
The paragraph explains how the discovery of hydrothermal vents and chemosynthesis changed biological understanding by demonstrating that life can exist without sunlight.
An effective conclusion must summarize this shift in biological understanding without introducing unrelated facts.
2
Evaluate the choices for grammatical correctness.
The option beginning with 'These deep-sea systems' contains a comma splice, and the option beginning with 'Consequently, the oceanographers' contains an inappropriate tense shift ('discover' in a past-tense context).
ACT English questions require the correct option to be grammatically correct as well as rhetorically effective.
3
Select the option that matches both the content goals and grammatical standards.
The option starting with 'Ultimately, the existence' successfully connects the discovery of chemosynthesis to the broader scientific shift away from sun-dependent life models, using correct grammar.
This choice resolves the paragraph's focus on the sun-free ecosystem and provides a strong, grammatically correct concluding statement.

Key Concept

Selecting Concluding Sentences and Transitions
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Topics

Selecting Concluding Sentences and Transitions

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