Question

There was nothing to do（ ） wait until he came back.

A.but
B.but to

答案选A，可是but前面是to do，根据平行结构，后面也应该是but to wait 呀。为什么选A呢？

Answer 1

当but/except解释为“除了”时，如果后面跟上动词，有两种情况，一种是用to +动词原形，另一种就是直接跟上动词原形。判定原则是这样的：
当but/except前有动词do这个词的任何一种形式的时候，在but/except后不加to，直接跟上动词原形；
当but/except前没有do这个词的时候，那么后面就要用to+动词原形。
如：He could do nothing but wait.
He had nothing to do but wait.
He had no choice but to wait.
另外，还有几个常用的短语也要记住：
can't but do; can't hlep but do 这两个短语都解释为“不得不做……
can't help doing 情不自禁做……；忍不住做……
can't hlep to do 不能帮助做某事
如：She can't help to clean the room because she's busy making a cake.
While shopping, people sometimes can't help being persuaded into buying something they don't really need.

Answer 2

因为和前面的do 共用了前面的to

Answer 3

A