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Question

Difficulty: EasySelecting Concluding Sentences and Transitions

In 1977, oceanographers exploring the Galapagos Rift made a startling discovery. Deep on the ocean floor, where no sunlight could penetrate, they found hydrothermal vents spewing superheated, mineral-rich water. Instead of finding a barren wasteland, they observed thriving ecosystems teeming with giant tube worms, blind crabs, and vast colonies of bacteria. These organisms did not rely on photosynthesis; instead, they survived on chemical energy through a process called chemosynthesis.

The writer wants to add a concluding sentence to the paragraph that wraps up the discussion of chemosynthesis and reinforces the main idea of the passage (that this discovery revealed a new way life can thrive without sunlight). Which of the following sentences best accomplishes this goal?

  1. This ground-breaking discovery proved that diverse life could flourish in the absolute darkness of the deep ocean.Answer
  2. B
    Hydrothermal vents are also found in the Atlantic Ocean, where scientists plan to conduct more studies in the future.
  3. C
    However, these ecosystems are very delicate, they can be easily disrupted by deep-sea mining.
  4. D
    Therefore, scientists will continue to study these vents and learned more about chemosynthesis.

Answer

This ground-breaking discovery proved that diverse life could flourish in the absolute darkness of the deep ocean.
The correct option successfully summarizes the paragraph's main focus by stating that this discovery proved that diverse life could flourish in the absolute darkness of the deep ocean, which directly wraps up the discussion of how chemosynthesis enables organisms to survive without sunlight.

Step-by-Step Solution

1
Analyze the paragraph's main idea and focus.
The paragraph describes the discovery of deep-sea hydrothermal vents where life thrives without sunlight using chemosynthesis.
To choose an effective conclusion, the sentence must align with the passage's main theme of life thriving in darkness.
2
Evaluate the options for transition logic and relevance.
The option showing that diverse life could flourish in the absolute darkness is highly relevant and summarizes the paragraph.
A good conclusion reinforces the main idea without introducing new, irrelevant information.
3
Check the remaining options for grammatical correctness and topical focus.
The other options either introduce new topics (Atlantic Ocean, deep-sea mining) or contain grammatical errors like comma splices and tense shifts.
An ACT conclusion must be both grammatically correct and rhetorically appropriate.

Key Concept

Selecting Concluding Sentences and Transitions
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Topics

Selecting Concluding Sentences and Transitions

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