OG 12/e SC:#59 choice D or E

[aagar2003]

I cannot reproduce the question as it is against the rules of the forum.

Can somebody please explain why is Choice (D) correct and not (E).

In, E is said to be wordy and awkward but I believe it is better than Choice (D).
Should not the explanation of this question should be more on idiomatic lines.

Helped X by Y
Helped X, for -> The use of comma to separate the second clause related to first should be incorrect?

[RonPurewal]

hi --

we appreciate your following the forum rules, but you've got to give us something to work with here.

if you are quoting a prohibited source, and you need to use an example to make a point, the best thing you can do is construct a sentence with similar grammar.
i.e., change the actual words of the sentence, but keep the grammar intact.