GWD-1-19

ecru

19. 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.

1. not caused by stress, alcohol, or rich foods, but
   
2. not caused by stress, alcohol, or rich foods, but are by
   
3. caused not by stress, alcohol, or rich foods, but by
   
4. caused not by stress, alcohol, and rich foods, but
   
5. caused not by stress, alcohol, and rich foods, but are by

请教：我选了B，现在看来B不对。如果改成but are caused by是不是就对了？

xuseraph

应该是c 吧， not by....but by.. 结构对称