Hey All,
Not to rain on the parade, but as far as I can see, this question has yet to be correctly explained in its entirety, so I thought I'd take it on.
In
MGMAT terms, this question has two major categories: verb tense and parallelism. You can see verb tense because the answer choices split in terms of tense. You can see parallelism because of the prominent "and" in the sentence.
The utility company has announced that it will permanently close its Unit I nuclear power plant, the first plant that had been built by private industry and the model for a generation of modern nuclear reactors.
(A) that had been built by private industry and
PROBLEM: "had been built" is the past perfect tense. You can only correctly use the past perfect tense if the sentence already has a past tense verb in it. This one doesn't. The problem isn't really parallelism so much as verb tense.
(B) built by private industry and which was
PROBLEM: Parallelism involves whatever words come after your parallel markers (in this case "and"). Here, we're given "which", which means there should also be a "which" in front of the first item in the list ("built by private industry). There isn't.
(C) to be built by private industry and which was
PROBLEM: Same as above.
(D) built by private industry and
ANSWER: "the first plant" and "the model" are allowed to be parallel here.
(E) to have been built by private industry and was
PROBLEM: Same as B and C.
Apologies if this question was already answered adequately, but I felt enough was missing it was worth giving my two cents. Good luck!
-t