All you have to do is do sth

问题描述:

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

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.