再问GWD-1-19，请大家过来响应一下

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

这题答案是C, 偶选了B.

1问：B为什么错呢？平行结构用的蛮好呀。

2问：C,D,E  中，be caused not by 不别扭吗？难道be not caused by 不对吗？

谢谢哪位nn帮忙解答一下？

这里考的是平行对称（ETS的老八股要求，不同于一般的语法要求）：我感觉考时“要能多平行，就有多平行”，哪怕在平行的结构中插入一个字有时都不被允许。因此C中的not by ... but by...是最佳答案。not caused by ...but are by...正是在前面插入了一词而破坏了平衡，而且后面的are冗余。

另外 be caused not by 中not作副词修饰by介词短语，语法上及逻辑上都没有问题。

可能我们还不太习惯这种表达方式，没关系，多念几遍形成语感就好了。楼上MM加油！

要能多平行，就有多平行

这句话太精辟了，总结了平行结构的真谛啊，谢谢mm. 强！

有道理！这位mm也强！

偶怎么想到它是和are比，所以就觉得B对了。谢谢哦。