GMAT Sentence Correction (SC) | Re: Because chickens lack teeth, they need another way to break

A)before reaching the stomach, and for this reason, chickens have a gizzard in which stones they swallow are used to grind their food-There is no subject for "before reaching the stomach"- So Eliminate.

B)before it reaches the stomach, and for this reason, chickens have a gizzard in which stones they have swallowed is used to grind their food-stones is plural, so the verb also has to be plural. But here it is singular (is)- So Eliminate.

C)before it reaches the stomach, and for
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