There were all so tired that they could A do nothing but sleep B do nothing but to sleep为什么选A而不选B呢?

问题描述:

There were all so tired that they could A do nothing but sleep B do nothing but to sleep
为什么选A而不选B呢?

but 前后是并列成分 do与sleep是并列成分

could接不带to动词原形.

这是一个句式
but后面接动词原形

这个就是固定用法 do nothing but (省略了to) do