<p>Well, it can’t be D because it changes the meaning and it doesn’t make sense. The original sentence is saying that the construction would have been completed, but it was postponed due to weather. D says that the construction has been completed, but it was postponed (contradictory).
B doesn’t work because of tense. E doesn’t work because construction isn’t plural and “nevertheless” makes its own independent clause. Not sure about A, but C has a bad conjunction.
In my opinion, it sounds better if they put the words “would have been completed” or something, but that’s probably a parallelism issue.</p>