Here is the text of the entire question:

A proposal has been made to trim the horns from rhinoceroses to discourage poachers; the question is whether tourists will continue to visit game parks and see rhinoceroses after their horns are trimmed.

A) whether tourists will continue to visit game parks and see rhinoceroses after their horns are
B) whether tourists will continue to visit game parks to see one once their horns are
C) whether tourists will continue to visit game parks to see rhinoceroses once the animals' horns have been
D) if tourists will continue to visit game parks and see rhinoceroses once the animals' horns are
E) if tourists will continue to visit game parks to see one after the animals' horns have been

Here, the pronoun "their" is ambiguous - it could refer to either "tourists" or "rhinoceroses."

In English, it is most often the case that a pronoun will most likely perform the same function as the noun (antecedent) that it replaced. For example: "Aliya bumped into Patricia, so she apologized." Because "Aliya" was the subject of the first clause, it is natural to assume that the "she," which is also a subject, should refer to Aliya. There is ambiguity, but "Aliya" has more claim to the pronoun "she" than "Patricia."

So in the above sentence, "tourists" are a subject, and "rhinoceroses" an object. Thus, the pronoun "their" in conjunction with the subject "horns" seems to point to "tourists." This is nonsensical.

Don't overthink the pronoun-at-beginning-of-clause thing, though. If you think that there's pronoun ambiguity, CHECK THE ANSWER CHOICES!

- if some have the pronoun, and some revert back to a noun, the GMAT is testing pronoun ambiguity
- if they all have the same pronoun, the GMAT isn't testing that
- if answer choices switch pronouns, it's testing pronoun agreement.

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