我告诉你个口诀:“有do,无to;无do,有to”,
在but的前面如果出现了do,did,does的话,but 后面的to就可以省略,
另外,此类的用法,还有except 和主系表结构,也是一样的.
e.g.They did nothing but wait.
She did nothing except look at the photo.
反过来,but的前面如果没有do,did,does,but 后面就用to
e.g.There is no choice but to wait.
主系表句型里:主语不带“do”,表语则用to
主语带“do”,表语的 to可用可不用
e.g.Your job is to reply emails from the customers.
The only thing I can do now is (to) go on by myself.
主语里的定语从句有个do