all I have to do is后面用动词原型还是to do?
我觉得is后面应该跟to do,但很多时候不是这样的,比如以下几句都是is 后直接跟动词原型,好象不合语法嘛：
All I have to do is do what I wanna do!
All i have to do is sign,and i'm free.
All I have to do is persuade him to go with us.
以下语句是跟to do的,这样才感觉比较合理：
From now on all I have to do is to held on.
All I have to do is to learn Chinese.
为什么2种都可以呢?