Multiple choice

Directions: The following question presents a sentence, part of which or all of which is underlined. Beneath the sentence you will find five ways of phrasing the underlined part. The first of these repeats the original; the other four are different. If you think the original is best, choose the first answer; otherwise choose one of the others.

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."

  1. crests and troughs that remain stationary although the air that forms them is moving rapidly, are

  2. crests and troughs that remain stationary although they are formed by rapidly moving air, are

  3. crests and troughs that remain stationary although the air that forms them is moving rapidly, is

  4. stationary crests and troughs although the air that forms them is moving rapidly, are

  5. stationary crests and troughs although they are formed by rapidly moving air, is
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The subject 'flow pattern' requires the singular verb 'is,' not 'are.' The long descriptive clause between commas ('with crests and troughs...') modifies the subject but doesn't change the fact that the main clause subject is singular. The core sentence structure is: 'the resulting flow pattern...is known as standing waves.'

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