(1)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 t ake 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.)
(2)时态
1) 现在时：一般现在时表示的动词,有时与谓语动词表示的动作同时发生,有时发生在谓语动词的动作之后.
He seems to know this.
I hope to see you again.= I hope that I'll see you again.我希望再见到你.
2) 完成时：表示的动作发生在谓语动词表示的动作之前.
I'm sorry to have given you so much trouble.
He seems to have caught a cold.
3) 进行时：表示动作正在进行,与谓语动词表示的动作同时发生.
He seems to be eating something.
4) 完成进行时：
She is known to have been wreaking on the problem for many years.
