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Question

Difficulty: HardSubject-Verb Agreement

In marine biology, researchers study how organisms adapt to extreme environments. The bioluminescent signaling of bathypelagic organisms, which serves to attract mates or deter predators in the pitch-black depths of the ocean's midnight zone, _______ a crucial mechanism for survival. Without these specialized chemical reactions, species would struggle to reproduce or avoid predation in the vast, lightless habitat.

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

  1. A
    constitute
  2. constitutesAnswer
  3. C
    are constituting
  4. D
    have constituted

Answer

The verb that correctly completes the sentence is the singular, present-tense verb 'constitutes', which agrees with the singular subject 'signaling'.
The subject of the sentence is the singular noun phrase 'The bioluminescent signaling'. The prepositional phrase 'of bathypelagic organisms' and the relative clause 'which serves to attract...' act as modifiers and do not affect the grammatical number of the subject. Therefore, the singular present-tense verb 'constitutes' is required to maintain subject-verb agreement.

Step-by-Step Solution

1
Identify the subject of the target sentence.
The subject is the noun phrase 'The bioluminescent signaling'. The head noun of this phrase is 'signaling', which is singular.
To ensure subject-verb agreement, the true subject must be isolated from any modifying prepositional phrases or clauses.
2
Analyze the intervening words between the subject and the verb.
The phrase 'of bathypelagic organisms' and the relative clause 'which serves to attract mates or deter predators in the pitch-black depths of the ocean's midnight zone' both modify the subject but do not change its singular number.
Standard English conventions dictate that intervening phrases or clauses containing plural nouns (like 'organisms' or 'depths') do not alter the number of the main subject.
3
Determine the correct verb form and tense.
The sentence presents a general, timeless scientific fact, requiring the simple present tense. Since the subject 'signaling' is singular, the correct verb form is the singular present-tense verb 'constitutes'.
Selecting a verb that matches both the singular number of the subject and the simple present tense of the surrounding context.

Key Concept

Subject-verb agreement requires a verb to match the number (singular or plural) of its grammatical subject, even when separated by intervening phrases or clauses containing nouns of a different number.
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Topics

Subject-Verb Agreement

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