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Difficulty: MediumSubject-Verb Agreement

The following passage is an excerpt from a science article:

Deep-sea hydrothermal vents, first discovered in 1977, support unique ecosystems that thrive in the absence of sunlight. The biological diversity of these remote habitats, which includes giant tube worms and ghost crabs, depend on chemosynthetic bacteria for survival. These microorganisms convert toxic hydrogen sulfide into organic matter, forming the foundation of the vent food web.

Which option is the grammatically correct replacement for the underlined word?

  1. A
    NO CHANGE
  2. dependsAnswer
  3. C
    depended
  4. D
    are depending

Answer

The option containing the singular present-tense verb 'depends' is correct.
The grammatical subject of the sentence is 'diversity,' which is singular. The prepositional phrase 'of these remote habitats' and the relative clause 'which includes giant tube worms and ghost crabs' are intervening descriptive elements that do not affect the grammatical number of the subject. Therefore, a singular verb is required. The present-tense singular verb 'depends' matches the subject and maintains the present-tense context of the surrounding sentences.

Step-by-Step Solution

1
Identify the true subject of the verb in the underlined portion.
The subject is the singular noun 'diversity.'
To ensure subject-verb agreement, the subject must be isolated from intervening elements. Here, 'of these remote habitats' (prepositional phrase) and 'which includes giant tube worms and ghost crabs' (relative clause) contain plural nouns, but they do not change the singular nature of the subject 'diversity.'
2
Determine the appropriate verb form based on subject number and tense consistency.
The singular, present-tense verb 'depends' is required.
A singular subject requires a singular verb. Furthermore, the passage is written in the present tense ('support,' 'convert,' 'forming'), meaning the present-tense form 'depends' must be used to maintain tense consistency.

Key Concept

Subject-Verb Agreement with Intervening Phrases
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Topics

Subject-Verb Agreement

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