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Difficulty: MediumSubject-Verb Agreement

Astronomers today continue to study these cosmic objects. The discovery of pulsars, which are highly magnetized rotating neutron stars, reveal how stars behave at the end of their life cycles.

Which of the following is the correct choice for the underlined portion?

  1. A
    NO CHANGE
  2. revealsAnswer
  3. C
    revealed
  4. D
    have revealed

Answer

reveals
The correct option is 'reveals' because the subject of the clause is the singular noun 'discovery'. The intervening structures 'of pulsars' and 'which are highly magnetized rotating neutron stars' contain plural nouns that must not affect the verb's agreement. The singular present-tense verb 'reveals' agrees with 'discovery' and aligns with the present-tense context established by the verbs 'continue' and 'behave'.

Step-by-Step Solution

1
Identify the grammatical subject of the clause containing the verb.
The subject is the singular noun 'discovery'. The prepositional phrase 'of pulsars' and the relative clause 'which are highly magnetized rotating neutron stars' both modify 'discovery' but do not change its grammatical number.
Verbs must agree with their actual subject, not with nouns inside modifying phrases or clauses that lie between the subject and the verb.
2
Determine the appropriate tense of the verb from the passage context.
The passage establishes a present-tense timeline using verbs like 'continue' and 'behave'.
Verb tenses must remain consistent unless a shift is logically required by the context.
3
Combine the subject number and verb tense to find the correct form.
A third-person singular, present-tense verb is needed, which is 'reveals'.
Matching both singular agreement and present tense resolves the grammatical error.

Key Concept

Subject-verb agreement requires a verb to agree in number with its grammatical subject. Descriptive elements like prepositional phrases or relative clauses that separate the subject from the verb must be ignored when determining agreement.
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Topics

Subject-Verb Agreement

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