The peaks of a mountain range, acting like rocks in a streambed, produ

This is one of those wordy GMAT sentences that probably has too many commas, so all of the answer choices basically “sound” the same. But in this case, there’s an easy elimination once you catch the subject-verb issue: after the semicolon, we have “the resulting flow pattern, [modifier blah blah], ARE known…”

That’s bad and wrong. (A) is out.


We can split some hairs over the differences between (A) and (B), but the subject-verb thing is a still a big, fat problem. (B) is out, too.


The subject-verb agreement is fine here, so that’s cool. We have perfect reasonable uses of the modifier “that” in both cases: “crests and troughs” are indeed the things “that remain stationary”, and “the air” is the thing “that forms them.” And “them” refers back to “crests and troughs.”

I don’t see any mechanical issues at all, so let’s keep (C).


Same subject-verb problem as in (A) and (B). I like free stuff, and this is basically free stuff. Thank you, GMAT, for taking mercy on us and letting us whittle this down to (C) and (E) in no time at all.


Hm, there’s nothing explicitly WRONG with (E) in terms of grammar. The pronoun is OK (“they” refers to “stationary crests and troughs”), and so is the subject-verb agreement.

As we mentioned in our long-winded beginner’s guide to SC, once you eliminate everything you can based on DEFINITE grammar rules, then you’ll want to compare the remaining pairs side-by-side to see if there’s any meaning difference between the two:

(C) crests and troughs that remain stationary although the air that forms them is moving rapidly, is
(E) stationary crests and troughs although they are formed by rapidly moving air

So what are the differences between these two? Well, (C) uses active voice (“the air that forms them is moving rapidly”), while (E) is passive (“they are formed by rapidly moving air”), and we could argue that the active voice is clearer and stronger in this particular case. (Though passive voice can be acceptable on the GMAT – but that’s a longer conversation for another day.)

More importantly, (C) does a better job of emphasizing the heart of the sentence. The thing that is (allegedly?) interesting about the crests and troughs isn’t simply that they are formed by rapidly moving air – and that’s basically what (E) says. The noteworthy thing is that the crests and troughs are stationary even though they are formed by rapidly moving air – and by putting the phrase “that remain stationary” right before “although the air that forms them is moving rapidly”, (C) emphasizes this fact much more clearly than (E) does.

Fun stuff. (C) is the best answer.