Gulf Asteroid

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Since the 1970s, scientists have believed that an asteroid once landed in the Gulf of Mexico and released ash causing a darkening of the sky by 10 to 20 percent over the ensuing decade, which inhibited photosynthesis and leading to the extinction of countless species on Earth.

Review: Gulf Asteroid


Explanation

Creating a filter: In this question, the original sentence has an error at the end of the underlined portion: "leading" should be the past tense verb "led" in order to be parallel with "inhibited."

Applying the filter: as we look at the answer choices after (A), we can focus first on the latter two verbs. Choice (B) fixes the problem with "led" but makes other changes; it replaces "which" with a phrase with the pronoun "it," which has ambiguous reference, so (B) is out. Choice (C) has parallel verbs with "inhibiting" and "leading," so it passes our filter. Choice (D) creates an ungrammatical structure in which "inhibited," in coming after a comma splice, has no grammatical verb, so (D) is out. Choice (E) is not parallel between "inhibiting" and "led." The correct answer is (C). 


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