All you have to do is do sth

题目

All you have to do is do sth
为什么是do sth?
而不是to do sth?

答案

All you have to do is do sth
=All [that] you have to do is do sth
这是不定式的典型用法之一：
作表语的不定式,前面有实意动词do的某种形式,要用省略to的形式.