carcass
So C and D. D seems correct grammatically (confirm this Mike please) but it is unecessary long and wordy. C is the best.
Dear
carcass,
I'm glad you like the question.
In addition to being too wordy,
(D) also messes up the idiom --- the idiom is simply "
both ... and", and the GMAT doesn't like adding any garnish to this idiom --- choice
(D) has "
both ... and also" --- while that's not grammatically incorrect, it's wordy and redundant, and the GMAT does not like it at all. Furthermore,
(C) has the action words as verbs (
reducing, eliminating), but
(D) has the action words as nouns (
reduction, elimination) --- as a general rule, if an action word appears both in a verb form and a noun form on the GMAT SC, the verb form will be more concise, more direct, and more powerful --- hence, almost always preferable on the GMAT SC. Technically, I guess
(D) is grammatically correct, but there are a few clear signs why it shouldn't be selected as the answer.
Does all this make sense?
Mike