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Difficulty: MediumParallel Structure

In their comprehensive study of deep-sea *Bathymodiolus* mussels, marine biologists observed that these resilient organisms survive in extreme hydrothermal vent environments by hosting symbiotic bacteria in their gills, filtering organic matter from the surrounding water, and ________ metabolic waste through specialized physiological pathways. This allows the mussels to thrive where few other species can.

Which choice completes the text so that it conforms to the conventions of Standard English?

  1. excretingAnswer
  2. B
    to excrete
  3. C
    they excrete
  4. D
    the excretion of

Answer

excreting
The sentence outlines three parallel activities through which mussels survive, using a list connected by the coordinating conjunction 'and'. The first two items are gerund phrases ('hosting...' and 'filtering...'). To maintain parallel structure, the final item must also begin with a gerund. The option 'excreting' correctly provides this parallel form.

Step-by-Step Solution

1
Identify the grammatical structure of the sentence and locate the list of items connected by the conjunction 'and'.
The sentence lists three parallel methods by which the mussels survive: 'hosting...', 'filtering...', and the final action starting at the blank.
This establishes that the items in the list must share the same grammatical form.
2
Analyze the grammatical form of the existing list items.
The first item starts with the gerund 'hosting', and the second item starts with the gerund 'filtering'.
Determining the parts of speech of the established items tells us what form the final item must take to be parallel.
3
Select the choice that starts with a gerund (verb ending in -ing) to complete the parallel series.
The gerund 'excreting' matches the forms 'hosting' and 'filtering', completing the series correctly.
Conforming to parallel structure is required by the conventions of Standard English.

Key Concept

Parallel Structure
Estimated Time:1m 0s
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Topics

Parallel Structure

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