The construction "Both...and" requires that the phrase following "both" be parallel with the phrase following "and." Not only must they be grammatically parallel, but they also must be comparable things. That means that the sentence is incorrect as written: "threatened by" is not parallel to "by increasing." (C) can also be eliminated for this reason; if "both" is followed by "because," "and" must be followed by "because" as well.

Choice (B) is incorrect because of verb tense issues. If the firm's projected net profits are "falling," that is happening in the present. But the falling profits "forced" a change. That's past tense. If the projected profits are falling, then "have forced" would be correct.

The main difference between (D) and (E) is the final clause: "forcing" or "which forced." The word "which" generally tells us that what follows modifies the immediately preceding word. However, in (E), it wasn't the "fifth consecutive quarter" that forced the change. Thus, "forcing" is accurate, as it modifies the previous verb, "fell." Choice (D) is correct.