GMAT Sentence Correction (SC) | Re: A proposal has been made to trim the horns from rhinoceroses

Still confused over A and C. I think pronoun ambiguity is not an issue here because humans cannnot have horns. Daagh well explained the difference between present perfect and present, however we do not know that information about whether the zoo plans to cut horns in a day or over a period of time. Experts, please elaborate whether there is further reasoning to picking C over A.

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