Bunuel
China
was united under the Qin and Han before Buddhism would have been introduced, united again four centuries later in the Tang Dynasty, a time now regarded as the "golden age" of Chinese Buddhism.
A. was united under the Qin and Han before Buddhism would have been introduced, united
B. had been united under the Qin and Han before Buddhism had been introduced, united
C. had been united under the Qin and Han before Buddhism was introduced, and it was united
D. was united under the Qin and Han before Buddhism had been introduced, and they were united
E. was united under the Qin and Han before Buddhism would have been introduced, and they had been united
Magoosh Official Explanation
Split #1a: what happens after the first comma? In all five choices, we have subject "China" and a bonafide verb, "was united" or "had been united" --- therefore, everything up to the first comma is an independent clause that would stand on its own as a sentence. We cannot simply follow the comma with another verb "united" --- Choices (A) & (B) make this mistake. We need a conjunction ("and", "but", etc.) before the next verb --- choices (C) & (D) & (E) each has the conjunction "and" after that comma, introducing a second independent clause. Two independent clauses joined by a conjunction is a perfectly valid structure.
Split #1b: In choices (C) & (D) & (E), the subject of each is a pronoun. Choice (C) has the singular pronoun "it" and choices (D) & (E) have the plural pronoun "they." What is the antecedent? China. Yes, there are many many people in China, but China itself is singular. The singular noun needs a singular pronoun. Choices (D) & (E) are incorrect because of this.
Split #2: verb tense. We have a wide variety of verb tenses & forms in this problem, in three places –(i) the first verb, right at the beginning of the underlined section; (ii) the verb after "Buddhism"; and (iii) the verb at the end of the underlined section. Consider these three events ---- (i) China of Qin & Han, before Buddhism; (ii) the arrival of Buddhism in China; and (iii) Tang Dynasty China, once Buddhism was already there. Even without knowing the details of Chinese history, clearly event (i) is much earlier than the other two. The way we show that one event is before another past event is to use the past perfect tense: "had been united." Only choices (B) & (C) have this correct choice for the first verb. For second verb, the hypothetical "would have been introduced" in choices (A) & (E) is incorrect: this implies that Buddhism never in fact arrived in China, which is not consistent with what the sentence says. We want to show that this event, the arrival of Buddhism in China, happened after the first event, and using the past perfect tense, "had been introduced," as (B) and (D) do, would not convey that. We need the simple past tense for this event, and only (C) has this. For the third event --- as we discussed in Split #1, choices (A) & (B) don't have a verb there at all. Choices (C) & (D) have the simple past tense, which is correct. Choice (E) has the past perfect, "had been united", which is definitely incorrect: the earliest event should use the past perfect, but definitely not the latest even in a past sequence.
For all these reasons,
choice (C) is the only possible answer.