5、动词不定式 1、不定式做主语一般表示具体的某次动作。 Tocompletethe30-storiedbuildinginoneyearwasquiteadifficulttask. Todothatimpliestakingresponsibility. 当主语较长，谓语较短时，常用it做形式主语，...
To complete the 30-storied building in one year was quite a difficult task.
To do that implies taking responsibility.
It is important for modern young people to master at least two foreign languages.
A. It is+形容词+(for/of sb.)+不定式，如：
It is not easy to catch fish with your hands only.
It is important for us young people to learn English and master it.
B. It is+名词+不定式
It is a pity to have to go without her.
C. It takes (sb.) some time +不定式
It takes me three hours to learn English each day.
不定式作表语常表示将来的动作，主语常常是表示意向、打算、计划的词(idea, task, purpose)等,如：
The most important thing for one’s health is to have plenty of exercise.
I like to go out for walks in the warm sunshine in spring.
She failed to finish the assignment in time, and she was worried about it.
不定式前加一个疑问代词（what, which, who, whom, whose）或疑问副词（where, when, how, why），以及连词whether构成特殊的不定式短语，其作用相当于一个从句，这样的不定式短语常常在某些动词后面作宾语。
I couldn’t decide which book to choose.
I can tell you where to get this book.
When to start the program remains undecided.
The question is how to put the plan into practice.
A.不定式作状语表示目的。或用于so as和in order之后，来强调这种目的。如：
To learn a foreign language well, you must make painstaking efforts.
B.不定式表示结果，特别是在so…as to, such…as to, only to…以及too…to等结构中的不定式表示结果。如：
She left her hometown with her beloved man, never to return.
No one is too old to learn.
Would you be so kind as to carry the luggage for me?
It is likely to rain today, for it is very cloudy.
I am willing to help you with your homework, for we are friends.
He asked you to call him at ten o’clock.
I’d never allow my children to behave like that.
当不定式在let, make, have, 感官动词后面作宾语补语时，不定式不带to。如：
Whenever something is wrong with you, please do let me know.
I will have the students write a passage about Internet.
His efforts to carry out the plan were successful.
There is no need to bother him with such trifles.
B.由only, last, next, 序数词或形容词最高级修饰的名词常用不定式作定语。如：
Mr Zhang is always the first man to arrive at the office and the last man to leave.
I don’t think he is the best one to do the work.
would rather…than（宁愿…也不），had better…（最好），can’t help but…（不得不），had rather…（宁愿），cannot but…（不得不，必然），may/might as well…（不妨），let alone（更不用说）。如：
I can’t help but wish that nothing would go wrong.
They had never seen such delicious food, let alone eat it.
9）不定式的完成式to have done表示在谓语动词之前已经发生的动作，而不定式的一般式to do表示动作将要发生。不定式还有其被动形式：to be done（表示将来的被动动作）和to have been done（表示过去的被动动作）。