Sentence Correction

[RiyaR]

20. Wind resistance created by opening windows while driving results in a fuel penalty as great or greater than is incurred by using air conditioning.
(A) as great or greater than is incurred by using air conditioning
(B) that is as great or greater than is incurred using air conditioning
(C) as great as or greater than that of using air conditioning
(D) at least as great as air conditioning's
(E) at least as great as that incurred by using air conditioning

According to me, theanswer should be C.But it was wrong

[Jim@StratusPrep]

What is the source of this question? There are a lot of grammatical mistakes. I would not try to gain anything from this question.