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Difficulty: MediumSubject-Verb Agreement

The restoration of medieval stained glass windows requires a delicate balance of art and chemistry. The accumulation of dirt, pollutants, and fungal growth on the glass surface have threatened to obscure the vibrant colors permanently. Conservators must carefully clean the panels before applying a protective microcrystalline wax coating.

Which option correctly completes the underlined portion of the passage?

  1. A
    NO CHANGE
  2. has threatenedAnswer
  3. C
    threaten
  4. D
    threatened

Answer

has threatened
The singular verb 'has threatened' is correct because it agrees in number with the singular subject 'accumulation'. The plural nouns 'dirt', 'pollutants', and 'growth' are objects of the preposition 'of' and do not determine the number of the verb. This choice also maintains present-tense consistency with the surrounding text.

Step-by-Step Solution

1
Identify the grammatical subject of the sentence containing the underlined verb.
The subject is the singular noun 'accumulation'. The plural nouns 'dirt', 'pollutants', and 'growth' are part of the intervening prepositional phrase 'of dirt, pollutants, and fungal growth' and do not affect the verb's agreement.
The subject of a sentence is never found within a prepositional phrase.
2
Select the verb form that agrees with the singular subject and matches the tense of the passage.
The singular present perfect verb 'has threatened' agrees with the singular subject 'accumulation' and maintains consistency with the present tense of the rest of the passage ('requires', 'must').
A singular subject requires a singular verb, and tenses should remain consistent across sentences unless there is a clear temporal shift.

Key Concept

Subject-Verb Agreement with Intervening Phrases
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Topics

Subject-Verb Agreement

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