The Correct Answer and Explanation is:
The correct choice is C) the bioswales have mitigated both street flooding and the resulting pollution of nearby waterways.
This question tests the grammatical rule concerning introductory participial phrases and modifiers. The sentence begins with the phrase, “By reducing the runoff flowing into city sewers,” which describes an action. For the sentence to be grammatically correct, the subject of the main clause that follows must be the noun that is actually performing this action. In this context, the bioswales are the things reducing the runoff. Therefore, the subject of the clause that completes the sentence must be “the bioswales.”
Let’s analyze the options based on this rule:
- Choice A is incorrect. The subject is “the mitigation.” Mitigation is the result of the action, not the agent performing it. It does not make sense to say that “the mitigation” is reducing the runoff. This creates a dangling modifier.
- Choice B is incorrect. The subject is again “mitigation.” Although “bioswales'” is present as a possessive noun, the grammatical subject of the clause is still the abstract noun “mitigation,” which cannot perform the action of reducing runoff.
- Choice D is incorrect. The subject is “both street flooding and the resulting pollution.” Street flooding and pollution are the problems being solved; they are not the agents reducing the sewer runoff. This is another example of a dangling modifier.
- Choice C is correct. The subject of this clause is “the bioswales.” This aligns perfectly with the introductory phrase. The bioswales are the things that reduce the runoff, and they are also the subject of the verb “have mitigated.” This choice creates a logical, clear, and grammatically sound sentence without any misplaced or dangling modifiers. The active voice construction (“the bioswales have mitigated”) makes the relationship between the agent and the action direct and unambiguous.
