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Question

Difficulty: MediumSubject-Verb Agreement

In the field of volcanology, continuous satellite monitoring of sulfur dioxide plumes emitted by active volcanoes ______ researchers to track shifts in magma movement. By measuring the concentration of these gases from orbit, scientists can detect impending eruptions days before they occur on the ground, thereby providing critical warnings to nearby communities.

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

  1. A
    allow
  2. allowsAnswer
  3. C
    are allowing
  4. D
    was allowing

Answer

allows
The singular verb 'allows' correctly agrees with the singular subject 'monitoring.' The plural nouns 'plumes' and 'volcanoes' are object of prepositions in the intervening phrase and do not affect the verb's form.

Step-by-Step Solution

1
Identify the subject of the target clause.
The subject is 'monitoring' (singular), not 'plumes' or 'volcanoes' (plural), which are part of the intervening prepositional phrase 'of sulfur dioxide plumes emitted by active volcanoes.'
Verb agreement is determined by the true subject of the clause.
2
Determine the correct tense and form of the verb to match the subject and context.
The passage describes a general fact in the present tense (using 'can detect' and 'occur'), so a singular, present-tense verb ('allows') is required.
To maintain subject-verb agreement and tense consistency throughout the passage.

Key Concept

Subject-verb agreement with intervening prepositional phrases and maintaining tense consistency.
Estimated Time:45s
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Topics

Subject-Verb Agreement

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