(1)时态
①一般式：动词不定式一般式表示的动作发生在谓语动词之后，有时表示同时发生.如：
I hope to become a university student this year.(to become发生在hope之后)
We often hear Dick play the piano in the next room.(play和hear同时发生)
②完成式：表示的动作发生在谓语动词所表示的动作之前.如：
I'm sorry to have kept you waiting.
We are too young to have seen the old society.
③进行式：表示的动作与谓语动词同时发生.如：
The teacher happened to be correcting our papers when I came in.
They seemed to be discussing something important.
(2)语态
如果动词不定式的逻辑主语是这个不定式所表示的动作的承受者，不定式一般要用被动语态形式，如：
It's a great honour to be invited to Mary's birthday party.(不定式作主语)
It was impossible for lost time to be made up.(不定式作主语)
I wish to be sent to work in the country.(不定式作宾语)
Can you tell me which is the car to be repaired (不定式作定语)
He went to the hospital to be examined.(不定式作状语)
在There be结构中，修饰主语的不定式可用被动，也可用主动，如：There are still many things to take care of (to be taken care of).但有时两种形式表达的意思不同，如：These is nothing to do now.( We have nothing to do now.) There is nothing to be done now.(We can do nothing now.)
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