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Difficulty: Very hardShifts in Construction

For decades, the migration patterns of the monarch butterfly baffled entomologists. Although researchers knew the insects traveled thousands of miles south each autumn, how they navigated to the exact same high-altitude forests in Mexico remained unclear. Modern studies reveal that monarchs use a solar compass, which adjusts for the time of day, and their descent is guided by magnetic cues.

Which of the following alternatives to the underlined portion is most grammatically correct and consistent with the tone and structure of the sentence?

  1. A
    and their descent is guided by magnetic cues.
  2. B
    and they will be guided by magnetic cues during their descent.
  3. and rely on magnetic cues to guide their descent.Answer
  4. D
    and by guiding their descent, magnetic cues are utilized.

Answer

and rely on magnetic cues to guide their descent.
The correct option maintains the active voice and parallel structure established in the first clause. By coordinating the present-tense verb 'rely' with 'use', the sentence maintains 'monarchs' as the single subject of both actions and avoids any shift in construction.

Step-by-Step Solution

1
Identify the subject and voice of the first main clause in the coordinate sentence.
The subject is 'monarchs' and the verb 'use' is active.
Establishing the initial structure of the sentence determines the parallel pattern that should follow.
2
Analyze the underlined portion for shifts in construction relative to the first clause.
The underlined portion shifts to a passive verb form ('is guided') and changes the grammatical subject to 'their descent'.
Identifying this shift reveals the error in construction and parallelism that needs correction.
3
Evaluate the choices to find the one that maintains consistency in both voice and subject.
The option containing 'rely on magnetic cues' maintains the active voice and allows 'monarchs' to remain the implied subject of the coordinate verb.
A coordinate predicate using the active-voice verb 'rely' perfectly parallels 'use', avoiding any awkward shifts in construction.

Key Concept

Shifts in Construction
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Topics

Shifts in Construction

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