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?