this one was tricky, especially for me, since I've went through and memorized a bunch of the idioms already so upon first sight I knew what I was looking for.
the idiom "not X but rather Y" seem to fit here but once you look at D, the wording of it is just awkward so that couldn't be it.
B changed the statements around a little bit in comparison to the other so that's out.
So you're down to A, C, and E.
In E, "gaining" doesn't really work. I don't know the right term for it but it doesn't sound right because I guess "gaining" is something that is continuing in present and in the context of this sentence it doesn't work.
A and C now.
In C, "did not" is cumbersome as compared to A, which just used "not"
Although both A and C sounded pretty damn right to be, it starts getting pretty technical and knit-picking once you get down to the nitty gritty. I ended up choosing A just because of that little bit.