Remember that sometimes the sentence comps say the same thing twice, with clues in one part and blanks in another, and your clues should be your anticipations. I've bolded what I think your anticipations should be below:
"...a visceral decision rather than a rational judgment; that is, it was not so much rational as visceral."
So you're looking for an answer with a rational...visceral pairing. Choice (D): "a deliberate...instinctive" fits that pairing very nicely.