81. 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
这里的平行是不是应该从not就开始。也就是说此句可以是not caused by.., but caused by... 或者 caused not by... ,but by...