MUCH MORE IMPORTANTLY—
this is fundamentally a PARALLELISM problem.
right now, you're ignoring parallelism, and instead trying to treat the problem as though it were a bunch of individual idioms that have to be memorized. this is precisely the WORST possible approach to take to GMAT sentence correction!
the problems are designed to depend AS LITTLE AS POSSIBLE on memorized prescriptions of what's "acceptable"/"unacceptable", and AS MUCH AS POSSIBLE on relationships and patterns, especially parallelism and agreement.
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in this problem, you do need ONE piece of knowledge:
"What impact will it have?" is a QUESTION. the words can only be written in that order if the sentence is actually a question (ending with "?").
if this is a noun phrase in a normal sentence—as it is here—then it's "what impact it will have" / "the impact it will have".
...but, if you've seen enough sentences vs. questions in written english (and paid attention to them), you'll have absorbed this difference.
the rest of the wrong answer choices—B, C, and D—can be eliminated entirely on the basis of non-parallelism.
thinking about ANYTHING else before you think about parallelism is a big, big mistake.