摘要： 复习动词不定式A.to do不定式作主语
1．单个不定式作主语，谓语动词用单数。
To play with fire is dangerous.
2.不定式作主语时，若结构较长，谓语较短，常用it作形式主语，而将真正
A.to do不定式作主语
1．单个不定式作主语，谓语动词用单数。
To play with fire is dangerous.
2.不定式作主语时，若结构较长，谓语较短，常用it作形式主语，而将真正的主语不定式放在后面。
It is our duty to take good care of the old.
B.to do不定式作表语
不定式作表语，表示将来要发生的动作。常用在系动词be, seem, appear, get, remain等后。
Your task today is to wash the curtains.
C.to do不定式作宾语
1．不定式可作某些动词的宾语，常见的动词有afford, agree, ask, decide, desire, expect, fail, hope, manage, promise, pretend, plan, intend, refuse, wish等。
We agreed to meet here but so far she hasn't turned up yet.
2．介词but/except后接不定式作宾语时，如果前面有实义动词do的任何一种形式，不定式就要省略to。
We could do nothing but wait for the next bus.
D.to do不定式作定语
不定式作定语常放于被修饰词之后，一般表示将来的动作；但修饰有序数词或形容词最高级限定的名词时，则表示已完成的动作。
The airport to be completed next year will help promote tourism in this area.
E.to do不定式作补足语
to do不定式可以充当一些动词后的宾语补足语；也可以作介词with后的宾补；还可以形成be said/thought/known/considered... to do这一结构。
The boy is said to have been admitted into a famous university in Qin Huangdao.
F.to do不定式作状语
to do不定式可以充当目的状语或意料之外的结果状语。
Anxiously, she took the dress out of the package and tried it on, only to find it didn't fit.
