Explanation

Creating a filter: the original sentence may sound a little funny but not be obviously in error. So we go to answer choice (B), ready to eliminate.

Finding objective defects: choice (B) is contrary to the sentence's intended meaning. In the meaning of the sentence, the campaigns have already shown promise, so the use of the future tense in (B) is not appropriate. Choice (C) has a similar problem: the final modifying phrase, with the word "disrupting," indicates that the intended meaning of this sentence is that startups are currently disrupting the industry, so the past perfect tense in the answer choice, "as had those startups," is contrary to intended meaning. Choice (C) is therefore out. Moreover, (D) and (E) have the same past/present mismatch, and are therefore out. We've eliminated all but one choice. The correct answer is (A).