英语语法高手来啊

在对话中为了避免和前面的动词重复，ought to可以省略后面的动词。像这样的动词还有be going to/be to /have to/ought to
例如：--Do you live here?
--No, but I used to.
但是如果不定式结构中的动词是be或have（have作“有”讲时），则需要保留动词be或have。
例如：--Are you a taxi-driver?
--No,but I used to be.

1. ought to在美国英语中，疑问、否定及简略答语中to可以省略：Ought I to go？Yes，you ought （to）.
You ought not (to) do that sort of thing.
Oughtn't we send for the police?
2.used to在简略句中也可以省略to：
I don't swim so often as I used (to).
Used he to go to the market every Sunday? No, he usedn't (to).
3.动词不定式符合to的省略：
A）当几个不定式并列时，除了第一个不定式外，其余的不定式常省略to：
I wished to finish my business and get away.
Do you want to have supper now or wait till later?
B)当want，like用于从句时（如when、if、what、as从句），为了避免重复用to代替上文的动作但也常常连同不定式符合to一起省略：
You may do the experiment with them if you want (to).
C)如果不定式是be或have，则通常要保留：
China is no longer what it used to be.
He hasn't finished yet. Well, he ought to have.
Aren't you the manager? No, and I don't want to be.

ought to 后的动词有不同的变形形式，如ought to do / be /have done 等等。ought to 其实是情态动词。如果ought to do 这里的do 都可以省，如果后是have done或者是 be 要省略到ought to have /ought to be