Source: Test Code (ETS) #37, Section 3 (sentence corrections), #9:

[Question deleted because paper tests are copyrighted and are not permitted to be reproduced online.]

Correct Answer: C. "but they can break these habits".
I chose answer A. "but these habits can be broken".

Answer choice A is passive versus active so I understand it is not preferred but it is still grammatically correct, I think. However, I didn't think answer choice C was correct because the pronoun is ambiguous. "they" can be referring to HABITS OR WRITERS. Can you please help me understand how C is the better answer choice?

Thank you!

I deleted the actual question but I think I can still address your question about the question :)

First, passive never trumps anything. It can only be chosen if every other choice has a grammatical error. (Same with concision, incidentally.)

Second, there is a little bit of fuzziness in terms of what the GMAT considers okay vs. ambiguous with respect to pronouns. In this case, you have two plural noun options: habits and writers.

So, my options to replace the pronoun "they" are:
but the writers can break these habits
or
but the habits can break these habits

If you had had another plural noun that could've fit here, ambiguity may have been a problem. But you can't credibly say "the habits can break the habits (themselves)."

For these types of issues (on which the GMAT itself has some fuzziness as to where it draws the line), I prefer to study from the newer questions (OG11 and the supplements) because things do change over time. The paper tests are at least 11 years old now (it was last given in 1997).

Ok, so concision and passive don't trump anything but unless everything is grammatically incorrect there is likely a better answer choice. I have two days remaining until my exam! I will stick with OG.

Thanks, Stacey.

you're welcome - good luck!