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?
问题描述：
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?
答
用TO DO一个句子中不能有两个动词
答
首先看看你前面三个句子的主语是All,
第1句“ All I have to do is do what I wanna do!”这句主语是All,"do what I wanna do"整个当作is的表语，所以不能简单的看成是be to de 的语法。
第2句的sign既可以作动词也可以作名词，单词本身具有双词性，此处很显然是名词。
对于最后2个句子，英语中 "be to do"就相当于“will do something”,表示的是个未发生将来的动作。
答
宝贝,根本不用考虑那么多,也不用听那么多的详解,我们老师讲过的,这就是一个固定搭配,后面永远加动词原形.记住就对了,有些东西是没必要解释的,因为那就是外国人的日常用法.