1.不定式做主语
(1)做形式主语的代词：
不定式做主语, 通常用it充当形式主语, 把做主语的不定式短语后置。 如：
It took me only five minutes to www.med126.com finish the job.
To be frank, it is a great relief to have the task fulfilled in so short a time.
(2)引导逻辑主语的介词：
不定式的逻辑主语一般由介词for引导,但下列表示人的性格行为特征的形容词做表语时, 不定式的逻辑主语则由of引导：
absurd, bold, brave, courageous, careful, careless, clever, wise, foolish, silly, stupid, good, nice, kind, thoughtful, considerate, greedy, generous, honest, modest, polite, rude, cruel, selfish, lazy, wicked, wrong。如：
Experts say walking is one of the best ways for a person to stay healthy.
It’s clever of you to have invented such a device.
(3)不定式做主语补足语：
掌握常用不定式做主语补足语的句型。注意不定式表示的动作发生的时间，并采用相应形式。如：
said
reported
thought
be to do sth.
believed
known
supposed
Byron is said to have lived www.med126.com on vinegar and potatoes.
The bank is reported in the local newspaper to have been robbed in broad daylight yesterday.
