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Question

Difficulty: Very hardSentence Reordering and Placement

[1] Until the late twentieth century, marine biologists assumed that all oceanic life ultimately depended on sunlight and photosynthesis for survival. [2] This paradigm was shattered in 1977 when researchers exploring the Galápagos Rift discovered thriving ecosystems surrounding hydrothermal vents on the ocean floor. [3] Instead of utilizing sunlight, these bizarre organisms relied on specialized bacteria that synthesized energy from the toxic chemical compounds spewed by the vents. [4] Such a process, known as chemosynthesis, demonstrated that life could flourish in the complete absence of solar radiation. [5] Today, astrobiologists study these extreme environments to model how life might exist on icy moons like Europa or Enceladus.

The writer wants to insert the following sentence into the paragraph:

'By oxidizing hydrogen sulfide, these microbes produce organic matter, forming the foundation of the vent food web.'

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

  1. A
    before Sentence 3
  2. before Sentence 4Answer
  3. C
    before Sentence 5
  4. D
    after Sentence 5

Answer

before Sentence 4
The correct placement is before the sentence starting with 'Such a process' because 'these microbes' in the inserted sentence refers directly back to the 'specialized bacteria' in the third sentence, and the description of oxidizing hydrogen sulfide explains the chemical reaction that the fourth sentence names 'chemosynthesis'.

Step-by-Step Solution

1
Analyze the target sentence for grammatical and logical markers.
The target sentence contains the plural demonstrative noun phrase 'these microbes' and describes a specific biological process ('oxidizing hydrogen sulfide... produce organic matter').
Identifying these clues helps locate their corresponding referents and context in the paragraph.
2
Find the logical antecedent for the phrase 'these microbes' in the paragraph.
Sentence 3 introduces 'specialized bacteria', which serves as the direct logical antecedent for 'these microbes'.
A pronoun or demonstrative phrase must follow the noun it references to maintain text cohesion.
3
Trace the logical connection for the biochemical process described in the target sentence.
Sentence 4 refers to 'Such a process, known as chemosynthesis'. The target sentence describes the actual chemical process that is named in Sentence 4.
The phrase 'Such a process' requires a prior description of the process to make logical sense.
4
Synthesize the placement position.
Inserting the sentence before Sentence 4 (and after Sentence 3) perfectly connects 'specialized bacteria' to 'these microbes' and provides the process described by 'Such a process' in Sentence 4.
This positioning preserves the logical narrative flow without creating gaps or misplaced references.

Key Concept

Logical sentence placement requires identifying key transitions, tracking pronouns to their antecedents, and placing descriptions of processes immediately before they are referenced or named.
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Topics

Sentence Reordering and Placement

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