mcelroytutoring
Yes, it sometimes sounds awkward when used correctly, but that does not make it any less correct. If the writers at the GMAC want to consider that an "idiom," then that's fine, and of course GMAT students should take note. But that doesn't mean that I have to personally agree with them.
Although if I were forced to choose, I still would select Choice B (prioritizing correct grammar over awkwardness), I would say that there is no correct answer to this question, because Choice B is awkward (albeit correct) and non-parallel, and Choice C is grammatically incorrect. GMAC says (emphasis mine) "Select the answer that produces the most effective sentence; your answer should make the sentence clear, exact, and free of grammatical error. It should also minimize awkwardness, ambiguity, and redundancy." I don't see an answer choice here that fits all of those descriptions.
Would you say "a group of exchange students are coming to visit."? No, you would say "a group of exchange students is coming to visit, because "a group" is the subject, not "students." What's the difference between "a group" and "a proportion?" Essentially, nothing.
I'm not sure how strongly you feel about this, so I'd like to leave the GMAT item writers/gods/human bit out.
You're welcome not to "personally agree with them", but you may be going overboard on grammatical concord. There are situations in which going "singular only" would be
unacceptable.
A majority are Russians.
A majority is Russians.mcelroytutoring
I know that a number of people disagree with me that B is best choice, especially since it would sound weird if I were to write, "a number of people disagrees with me." However, that which is grammatically correct is not always that which sounds best.
mcelroytutoring
The noun here is "proportion," not "women," because "women" is preceded by a preposition ("of") and is thus an object, not a subject. "proportion (of women) works" = "it works" = correct. Thus, "works" should be the correct verb, not "work."
I'm not sure how these statements can be defended.
A number of is used here as
many, and going plural on
a number of people is, in fact, correct. Going plural on
an overwhelming proportion of women is also correct. The point you make about appearing to be pedantic ("It is I/me") is secondary, because I don't think the GMAT would lose if this went to a usage panel.
Also, the (extremely broad) conclusion that "Ultimately, on this test, it doesn't matter what's technically and/or grammatically correct" is uncalled-for. The GMAT does not have a secret set of rules. There is almost complete overlap between what the GMAT tests and what is widely considered acceptable (if formal) usage.