Bunuel
The cardinals remained in the Sistine Chapel for far longer than the Vatican reporters expected,
which suggests that the deliberation over the new pope was both spirited and contemplative.
A. which suggests that the deliberation over the new pope was both spirited and contemplative
B. which suggests that the deliberation over the new pope both was spirited and contemplative
C. a situation suggesting the deliberation over the new pope was both spirited and it was contemplative
D. suggesting that the deliberation over the new pope was both spirited and contemplative
E. suggests that the deliberation over the new pope was both spirited and contemplative
Veritas Prep Official Explanation
You should quickly see that this problem provides you with a decision between three types of modifiers: relative modifiers (A and B), an end-of-sentence participial modifier (D), and an end-of-sentence appositive modifier (E). Importantly, relative modifiers (such as "which") are very restrictive: they must modify the noun (or noun phrase) that comes immediately before them. And here there is no noun for "which" to modify, so A and B cannot be correct.
The modifiers for C and D each work. Participial, -ing modifiers at the ends of sentences are allowed to modify the entire preceding clause, and are not restricted to simply the noun prior. Similarly, appropriate appositive phrases (such as "a situation..." here) at the ends of sentences are allowed to modify the preceding clause: here since the preceding clause is, indeed, a situation, this appositive is correct.
Once you move past the modifier decision, you should see that E is the outlier in that it is not a modifier; "suggests" is an active verb, and here that creates a comma splice error. "suggests" does not have a noun to be paired with, so this choice creates an incomplete sentence and is incorrect.
Between C and D, look at the major difference, which appears around the construction "both...and." Choice C provides a not-parallel construction: since "spirited" (an adjective) comes right after both, the portion after "and" should be parallel with another adjective. The addition of "it was" (a subject-verb construction) breaks that parallelism and makes C incorrect. The correct answer is D, which uses a proper modifier and a proper parallel construction.