China currently operates the world's second largest economy, and they

Magoosh Official Explanation:

Split #1: the pronoun, "they" vs. "it". Yes, there certainly are a great number of people in China, but these people do not explicitly appear in the sentence. In fact, no plural noun appears anywhere before the underlined part of the sentence. The subject is "China", and this is singular, so the adjective referring to it must be singular as well. This is a classic GMAT mistake, using the plural pronoun "they" for a population or constituency that is implied but not mentioned. On the GMAT, every pronoun must have a clear and unambiguous antecedent explicitly appearing somewhere in the sentence. The "it" in (D) & (E) is correct, and the "they" in (A) & (B) & (C) is not correct.

Split #2: "compared to" vs. "among". If I say "X compared to Y", I am implying those are two different, mutually exclusive groups --- "cats compared to dogs", "football players compared to concert violinists", "sumo wrestlers compared to ballerinas", etc. If I say "X among Y", I imply that X is member of the set Y --- "Abraham Lincoln among US Presidents", "Earth among the planets", "San Francisco among cities in California", etc. Which do we need here?

Here, the two terms are "growth rate" (i.e. of China) and "the world's major economies" --- not quite the same thing. If we take the "compared to" route, we would need to compare like-to-like, "growth rate [of China] " to "growth rates of other countries", which we could abbreviate to "that of" other countries. (B) & (E) don't include the phrase "that of": it compares the "growth rate" of China's economy to the whole of other economics: incorrect comparisons. ---- Furthermore, when we don a comparison, we need two mutually exclusive terms. We can't compare "China" to "nations of the world", because China is included in nations of the world. We need the crucial word "other". Thus, the whole correct construction would be "compared to that of the world's other economies" --- (A) does contain the word "other". Thus, of the three answers that take the "compared to" route, (A) & (B) & (E), none of them get all the correct pieces operating together. The correct format would be "compared to that of the world's other major economies", but that doesn't appear as a choice.

The other route would be the "among" route. When we use "among", we don't need two mutually exclusive groups --- "China among world nations" makes perfect sense. Furthermore, we can talk about a part among a whole --- China's economy's growth rate is part of China's economy overall, so it's a part of what's included in the whole of "the world's economies" --- therefore, it's perfectly correct to say "the fastest growth rate among the world's economies". This is precisely what (C) & (D) have.

Because of these splits, only (D) can be the answer.