GMAT Sentence Correction (SC) | Re: Since the 1970's, scientists have believed that an asteroid once

Since the 1970's, 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 the earth.

A) 'Which' is incorrect.

B) that an asteroid and that released - doesn't make sense..

C) asteroid landed ......... and released ash................., correct verb usage
inhibiting and leading ..... correct modifier
...

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