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.
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Dear Friends,

Here is a detailed explanation to this question-

Meaning is crucial to solving this problem:
Understanding the intended meaning is key to solving this question; the intended meaning of this sentence is that the peaks of a mountain range produce ripples in the air flowing over them, and the resulting flow pattern includes crests and troughs that remain stationary although the air that forms them is moving rapidly and is known as "standing waves."

Concepts tested here: Meaning + Subject-verb Agreement

A: This answer choice incorrectly uses the plural verb “are” to refer to the singular noun phrase “flow pattern”.

B: This answer choice incorrectly uses the plural verb “are” to refer to the singular noun phrase “flow pattern”.

C: Correct. This answer choice correctly uses the singular verb "is" to the singular noun phrase “flow pattern”. Further, Option C uses the phrase "crests and troughs that remain stationary although the air that forms them is moving rapidly", conveying the intended meaning - that the peaks of a mountain range produce ripples in the air flowing over them, and the resulting flow pattern includes crests and troughs that remain stationary although the air that forms them is moving rapidly and is known as "standing waves."

D: This answer choice incorrectly uses the plural verb “are” to refer to the singular noun phrase “flow pattern”. Further, Option D alters the meaning of the sentence through the phrase “stationary crests and troughs although the air that forms them is moving rapidly”; the construction of this phrase leads to an incoherent meaning; the intended meaning of this sentence is that the peaks of a mountain range produce ripples in the air flowing over them, and the resulting flow pattern includes crests and troughs that remain stationary although the air that forms them is moving rapidly and is known as "standing waves."

E: Trap. This answer choice alters the meaning of the sentence through the phrase “stationary crests and troughs although they are formed by rapidly moving air”; the construction of this phrase leads to an incoherent meaning; the intended meaning of this sentence is that the peaks of a mountain range produce ripples in the air flowing over them, and the resulting flow pattern includes crests and troughs that remain stationary although the air that forms them is moving rapidly and is known as "standing waves."

Hence, C is the best answer choice.

All the best!
Experts' Global Team
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This is how I approached the question:

"the resulting flow pattern" is singular and a singular verb should follow. Options A, B & D are out since they use "are" instead of the singular verb "is" for "the resulting flow pattern"

Between C and E.
C illustrates the contrast in a much concise and clear manner.

Option C - "X and Y" that remain stationary although the air that forms "X and Y" is moving
Option E - stationary "X and Y" although "X and Y" formed by rapidly moving air

Hence Option C is the best choice.


------If you like my explanation, consider giving me kudos-------

The peaks of a mountain range, acting like rocks in a streambed, produce ripples in the air flowing over them; the resulting flow pattern, with crests and troughs that remain stationary although the air that forms them is moving rapidly, are known as "standing waves."

A. crests and troughs that remain stationary although the air that forms them is moving rapidly, are The subject is “flow pattern”, which is singular. So the plural verb “are” cannot be used.

B. crests and troughs that remain stationary although they are formed by rapidly moving air, are The subject is “flow pattern”, which is singular. So the plural verb “are” cannot be used.

C. crests and troughs that remain stationary although the air that forms them is moving rapidly, is The correct verb "is" has been used and the intended meaning is clear.

D. stationary crests and troughs although the air that forms them is moving rapidly, are The subject is “flow pattern”, which is singular. So the plural verb “are” cannot be used.

E. stationary crests and troughs although they are formed by rapidly moving air, is Grammatically, this option is correct. But the focus of the main sentence is that crests and troughs are stationary even though they are formed by rapidly moving air. Option E is more in keeping with the original sentence.

- Nitha Jay

E. stationary crests and troughs although they are formed by rapidly moving air, is

This option omits the restrictive relative clause "that remain stationary". One of the requirements of a restrictive clause is that the sentence wouldn't make sense or mean the same thing without it. In this case, "although they are formed by rapidly moving air" is providing a counterpoint without having a main point to counter.

Maybe another example would illustrate this best:

Bananas that are yellow are tastiest although brown ones are good for baking. <--Correct
Bananas are tastiest although brown ones are good for baking. <--"Awkward and unclear" as OG-11 would put it

Use of although is the key here. It should be contrasting two things which is clearly visible in C and not in E.

Take away -->

1) "although" needs to be used to contrast two parallel noun phrases or phrases. "X although Y" X and Y needs to be in parallel
2) One of the requirements of a restrictive clause is that the sentence wouldn't make sense or mean the same thing without it."That remains stationary"

About 'E'

E. stationary crests and troughs although they are formed by rapidly moving air ,is

its unnecessary passive and it changes the meaning as well

I will not go beyond saying that C is more wholesome than E. I would not say. E is awkward or E lacks contrast. As long as the three elements are there namely, stationary on one side, rapidly moving on the other side and the contrast –marker 'although' in between, then I feel the contrast is established. The only faint reason why C was weighed in might have been because ‘the crests and troughs that remain’ is parallelly matched by ‘the air that forms’

How can we dispute an OG OA!
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The subject here is "resulting flow pattern", which is singular. Therefore, the verb that comes after the modifying phrase, 'with crests...' must be is. Eliminate (A), (B), and (D).

Next, we have this awkward phrase in (E): 'stationary crests and troughs although...' The 'although' signals a contrast, but what exactly is being contrasted. With (C), we have crests and troughs that remain stationary.' Now there is a clear need for 'although', because we want to contrast the way that the crests and troughs move with the way that the air below them moves.

Thus the answer is (C).
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I will try to break the tie between C and E.

Although rule : The pronoun after although does not refers to the nearest noun, but to the first noun in the sentence.

The sentence with option E is:
the resulting flow pattern, with stationary crests and troughs although they are formed by rapidly moving air, is known as “standing waves.”

According to the above rule, they refers to resulting flow pattern and not to stationary crests and troughs.

Hence, C wins.

i know C is correct by looking for the reason why E is wong.

Hi aditya,

Thanks for posting this question. This is a very nice question that once again exemplifies the importance of understanding the meaning and noting when a choice may change the meaning of the sentence.


Lets first analyze the original sentence -

The peaks of a mountain range, acting like rocks in a streambed, produce ripples in the air flowing over them; the resulting flow pattern, with crests and troughs that remain stationary although the air that forms them is moving rapidly, are known as "standing waves".

The peaks produce ripple in air. This creates a flow pattern. This flow pattern has crests and troughs. Even though the air that forms them moves rapidly, these remain stationary. This pattern is called standing waves.

Now given this meaning, lets focus on choice C - It communicates exactly the same thing. So C is the correct answer.

Now lets look at choice E - here the use of modifier - stationary- distorts the intended meaning. Now the intended contrast is not very apparent. It is no longer clear. Per choice A and C, the contrast is very clear - crests and troughs REMAIN stationary, whereas the air that forms them moves rapidly. But in choice E - it appears as if the stationary crests and troughs are made by the rapidly moving air.

This is why choice E is not correct.

Hope this helps. Let us know if you have any other questions about this.
Thanks.
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Good question to practice.

First split: "IS" or "ARE"?
the main subject of the second clause is "the resulting flow" that is singular ==> "IS" is correct ==> A, B, D are out immediately.

Second split: C or E?
Note: Many folks say E is wrong because of passive voice. The idea is WRONG. GMAC never says passive voice is always wrong. if you ALWAYS eliminate passive voice in real tests, you may get the question wrong.

Back to C and E.
to pick a correct answer, we need some basic grammars of using "although".
"Although" is used to convey contrast meaning between two parts of the sentence. The two MUST be parallel in meaning.
For example:
1/. I ate two green apples although they are mature. <== WRONG.
The blue part and the red part do NOT create a contrast meaning at all. The fact "I ate two green apples" and "they are mature" do not convey the intended contrast meaning.

2/. I ate two apples that are green although they are mature <== CORRECT.
The two blue parts are perfectly contrast: apples are green although they are mature.
Hence, the sentence is correct.

Compare C and E.
Option C: the resulting flow with [crests and troughs that remain stationary although the air that forms them is moving rapidly],is...............
The two blue parts are perfectly contrast and parallel in meaning. I used [....] to separate the sentence in which "although" is used correctly.

Option E: the resulting flow with stationary crests and troughs although they are formed by rapidly moving air , is.............
The red and the blue parts do NOT convey contrast. Thus, E is wrong.

Hope it helps.

Hi,

In C "remain stationary" seems redundant like "prices rise up". Am I missing something?

OK, this is weird: I just finished a conversation about this exact question a few minutes ago... with somebody else in NYC! I'd wonder if it was you, but your GMAT scores are different.

There are some 100% clear cases of redundancy in GMAT questions. You sometimes see things like this on actual SC questions:

• Every year, the the government spends over $4 trillion annually...
• The government program enabled consumers who want to purchase their first home to be able to do so with only a minimal down payment...

Those are unambiguously, horrifically redundant, right? There's zero doubt that they're wrong.

I don't think that's true of the phrase "remain stationary", though. "Remain" and "stationary" certainly aren't synonyms for each other, and we could easily use the word "stationary" without implying that something remained stationary over time:

• After sprinting downfield, Ronaldo was momentarily stationary as he watched the ball sail into the goal.
• Upon seeing his shockingly high GMAT score, Souvik became stationary for a few seconds, then gasped and jumped up and down with excitement.

So I would argue that the word "remained" absolutely tells us something that we wouldn't have otherwise known for certain: the crests and troughs were stationary for an extended period of time, not just for a moment.

I hope this helps!
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A, B and D: the resulting flow pattern...are
Here, are (plural) does not agree with pattern (singular).
Eliminate A, B and D.

Only PARALLEL FORMS may be compared.
E: stationary crests and troughs although they are formed by rapidly moving air
Here, a MODIFIER (stationary) is illogically compared to an ACTION (are formed by rapidly moving air).
Eliminate E.



OA: crests and troughs that remain stationary although the air that forms them is moving rapidly
Here, one ACTION (remain stationary) is logically compared to another ACTION (is moving rapidly).
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I completely understand why the answer choice must be option C but I still have one doubt. Option C is more wordy than Option E and both are grammatically correct too. Is there any other reason why option E is not a correct answer

kinshuk97gupta We can generally rely on all the wrong answers in an official question to be genuinely wrong, and E is no exception.

The "although" modifier that appears in all 5 choices is adverbial. That means it needs to modify an action, not a noun. So it can modify "remain stationary," but not "stationary crests and troughs."
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GMATNinja Sir, VeritasKarishma Ma'am

I have two doubts.

1. Why verb tense for answer C is not wrong. Should we not use simple present tense- Air that forms them moves rapidly.

2. Can we eliminate E for the fact "although" is contrasting noun with an action and not contrasting action with another action.

Please share your two cents.