GWD1-19

maylovehe1

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

maylovehe1

Answer is C. But why not B?

eilleenliu

这是一个考对称的吧~

not by...but by...

by 后面的结构要完全一致~