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

Source: Official Guide