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GMATPrep Q&A: Tackling a Tough Sentence Correction Question

Posted in Test Prep on November 16, 2010 by

We get a lot of interesting questions from Knewton students about GMATPrep® problems. Today, we’ll take a look at a particularly tricky Sentence Correction question dealing with comparisons, modifiers, and pronouns.

The stars, some of them at tremendous speeds, are in motion just as the planets are, yet being so far away from Earth that their apparent positions in the sky do not change enough for their movement to be observed during a single human lifetime.

(A) The stars, some of them at tremendous speeds, are in motion just as the planets are, yet being
(B) Like the planets, the stars are in motion, some of them at tremendous  speeds, but they are
(C) Although like the planets the stars are in motion, some of them at tremendous speeds, yet
(D) As the planets, the stars are in motion, some of them at tremendous  speeds, but they are
(E) The stars are in motion like the planets, some of which at tremendous speeds are in motion but

Take a shot at the problem on your own, then take a look at the explanation below to see how you did.

Explanation:

When looking at this question, you should first try to identify whether the original sentence is grammatically correct. In this case, the original sentence is not correct, for several different reasons. Since “at tremendous speeds” refers to the way that the stars are in motion, this modifier has to come at the end of that phrase to make sense.

“Some of them at tremendous speeds” is something called an absolute phrase. An absolute phrase is a noun phrase that is almost exactly like an appositive, only it doesn’t modify a particular noun; it modifies the ENTIRE previous clause. If this phrase were an appositive, then placing it after “the stars” would be correct. However, because it is an absolute phrase, it needs to come at the beginning or the end of the clause that it modifies, not right in the middle of it. This sentence is also a fragment because “yet” is a coordinating conjunction and must be followed by an independent clause, but in this case it is followed by the participial phrase “being so far away from Earth.” Therefore, answer choice A is incorrect.

Choice C is incorrect because “although… speeds” is a dependent clause, so the sentence does not have a main verb. D is incorrect because it uses “as” to compare two nouns: “the planets” and “the stars.” E is incorrect because “some of which at tremendous speeds are in motion” is convoluted and, as a relative clause, refers to “planets” instead of “stars,” changing the meaning of the sentence.

This leaves answer choice B. B is correct because “like” is used to compare two nouns: “planets” and “stars.” “Some of them at tremendous speeds” now correctly acts as an absolute phrase, modifying the entire clause “the stars are in motion.” In addition, we have an independent clause after the comma + “but.” Although it may seem that the pronoun “they” is ambiguous and could refer to either the “planets” or the “stars,” the reference is actually clear because the subject of this sentence is “stars” and the whole sentence is about stars.  Planets are just a kind of “throw-away” comparison here.

Correct Answer: B

GMATPrep® problem appears courtesy of the GMAC.