The Peaks of a Mountain Range, Acting like Rocks in a Streambed

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

“The peaks of a mountain range, acting like rocks in a streambed" - is a GMAT sentence correction question. This particular GMAT sentence correction topic has been taken from the book ‘GMAT Official Guide Verbal Review 2019’. This question checks Meaning, Tenses, and Grammatical Construction. GMAT Sentence Correction questions comprise 11-16 questions to be completed within 65 minutes. Each Sentence Correction question contains a sentence with an underlined portion that includes 0-2 errors.

Answer: C
Explanation: The following concepts are tested here:

1. Meaning
2. Subject-verb agreement

Hypothesis: The supposed meaning is key to solving this question. The meaning of this sentence states that the peaks of a mountain range deliver ripples in the air. The flow pattern includes crests and troughs that remain stationary although the air that forms them is moving rapidly and is known as "standing waves."

Option A: Incorrect.

In this statement, the plural verb “are” is used in an incorrect way. It refers to the singular noun phrase “flow pattern”.

Option B: Incorrect.

In this statement, the plural verb “are” is used in an incorrect way. It refers to the singular noun phrase “flow pattern”.

Option C: Correct.

In this statement, the singular verb “is” is used in the correct way. It refers to the phrase “flow pattern”. Option C uses the phrase "crests and troughs that remain stationary although the air that forms them is moving rapidly" which refers to the peaks of a mountain range that produces ripples in the air flowing over them. Additionally, “the resulting flow pattern” signifies crests and troughs which remain stationary. Lastly, these forms when moving rapidly are known as "standing waves."

Option D: Incorrect.

In this statement, the plural verb “are” is used in an incorrect way. It refers to the singular noun phrase “flow pattern”. Option D changes the meaning of the sentence. The phrase “stationary crests and troughs although the air that forms them is moving rapidly” directs to a confusing meaning. 

Option E: Incorrect.

Option E changes the meaning of the sentence. The phrase “stationary crests and troughs although the air that forms them is moving rapidly” directs to a confusing meaning. 

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