[Deleted because this question is from a banned source - see below.]

Can you please explain why A is correct and a better choice than D? I somewhat understand that D states that the agronomists will raise agricultural staples, which is obviously incorrect. But isn't 'reversion to the raising of agricultural staples' incorrect? Can you shed some light? Thanks.

Please cite the source of the question; if you don't, we'll have to delete the post. (And we won't answer it unless the author is cited!) Thanks.

I believe that the source is testmagicforum.com

Same deal as the other one - you can't cite a forum as a source. You have to find out where the question originally came from, because a couple of original sources (such as kaplan and scoretop) are banned here.

[Deleted because this question is from a banned source.]

A: correct, reversion to the raising(noun) is correctly used. infinitive does not fit here because there is no purpose to raise the staples.
B,C:reversion back redundant
D: use of infinitive doesn't fit
E: reversion into wrong idiom???