GMAT Sentence Correction (SC) | Sixty-five million years ago, according to some scientists,

Sixty-five million years ago, according to some scientists, an asteroid bigger than Mount Everest slammed into North America,which, causing plant and animal extinctions, marks the end of the geologic era known as the Cretaceous Period.

A. which, causing plant and animal extinctions, marks - Relative pronoun which can only modify nouns; Verb-ing causing plant and animal extinctions is misplaced
B. which caused the plant and animal extinctions marking - Relative pronoun which can only modify
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