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Difficulty: HardVerb Tense and Consistency

Although lacking a brain or nervous system, the slime mold *Physarum polycephalum* exhibits a form of primitive intelligence. When placed in a maze with oatmeal at two opposite ends, the single-celled organism spreads out to explore all possible paths. Within hours, it retracts its dead-end branches and concentrated its mass along the shortest route between the food sources. This behavior demonstrates that even simple organisms can process spatial information and optimize resource transport.

Which choice best maintains a consistent and logical verb tense throughout the passage?

  1. A
    NO CHANGE
  2. concentratesAnswer
  3. C
    concentrate
  4. D
    concentrating

Answer

The correct answer is concentrates, which is the singular present tense form of the verb.
The verb 'concentrates' correctly maintains the present tense established by the parallel verb 'retracts' in the compound predicate, as well as the other verbs throughout the passage ('exhibits', 'spreads', 'demonstrates') describing the general behavior of the organism.

Step-by-Step Solution

1
Identify the subject of the underlined verb and examine the sentence structure.
The subject of the underlined verb is the singular pronoun 'it'. The sentence contains a compound predicate joined by 'and', where 'it' performs two actions: 'retracts its dead-end branches' and the underlined action.
Understanding the subject and sentence structure helps identify the grammatical expectations for the verb, including subject-verb agreement and parallel construction.
2
Analyze the tense of the first verb in the compound predicate and the surrounding verbs in the passage.
The first verb in the compound predicate is 'retracts', which is in the present tense. Other verbs in the passage ('exhibits', 'spreads', 'demonstrates') are also in the present tense, establishing a scientific present-tense context.
To maintain verb tense consistency, verbs that share a subject in a compound predicate or occur within the same narrative context must stay in the same tense unless there is a logical reason to shift.
3
Evaluate the choices to find the form of the verb that is singular, present tense, and maintains parallel structure.
The singular present tense form 'concentrates' maintains parallel structure with 'retracts' and agrees with the singular subject 'it'.
This choice resolves the inconsistent past-tense shift in the original sentence without introducing agreement or structural errors.

Key Concept

Verb Tense and Consistency
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Topics

Verb Tense and Consistency

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