Sentence Correction

can anyone help me out ....

Recently physicians have determined that stomach ulcers are not caused by stress, alcohol, or rich foods, but a bacterium that dwells in the mucous lining of the stomach.
A. not caused by stress, alcohol, or rich foods, but
B. not caused by stress, alcohol, or rich foods, but are by
C. caused not by stress, alcohol, or rich foods, but by
D. caused not by stress, alcohol, and rich foods, but
E. caused not by stress, alcohol, and rich foods, but are by

I m guessing its ans should be C.

can u ppl verify it.

IMO the ans should be C

In solutions D and E, the use of the word "and" changes the meaning of the sentence. "stress, alcohol, and rich foods" implies that ulcers are caused by all three things working together, when the original intent of the sentence is that each factor can cause an ulcer by itself.

Between A, B, and C, look for parallelism. "not by...but by...." only C is parallel

caused not by X , but by Y

d/e- change the meaning of the sentence.
a- not a parallel construction

Could somebody expalin all the answer choices?
Whats wrong wit B? ARe" should not be included ?

"not A or B" means there is nothing

"not A and B" mean there is no A and B at the same time. Maybe,
there is A, not B
or there is B, not A
or there is nothing.

you can see "comprehensive grammar" for this matter.