他年龄小，没有见过那场血腥的战争。

(3)不定式作原因状语。主要用在表示喜怒哀乐等情感的形容词或过去分词后。

I am very sorry to hear that your mother is ill.

听到你母亲病了，我很难过。

即时跟踪1

(1)写出下列句子中不定式(短语)所作的成分

①To love and to be loved are the greatest happiness one can seek.主语

②I can't afford to buy the house.宾语

③His job is to teach English.表语

④I believe him to be honest.宾补

⑤He worked hard to pass the exam.目的状语

(2)用所给动词的正确形式填空

①The ability to express(express) an idea is as important as the idea itself.

②Father will not allow us to play(play) in the street.

③To stay(stay) warm at night，I would fill the woodstove，then set my alarm clock for midnight so I could refill it.

三、复合结构不定式

"for＋名词(或代词宾格)＋动词不定式"即构成复合结构的动词不定式。其中for本身无意义。for后面的名词或代词是不定式的逻辑主语，这种不定式在句中可作主语、表语、宾语或状语。

It is very important for us to get everything ready for the harvest.

为收获的季节准备好一切对我们来说很重要。

当作表语用的形容词表示不定式的逻辑主语的性质或特征时，就用介词of而不用for引出不定式的逻辑主语，这些形容词一般有good，nice，kind，wise，silly，stupid，foolish，right，wrong，careless，impolite等。

It is very kind of you to help him every day.

你真是太好了，每天都帮他。

四、but＋不定式

1.不定式在介词but，except，besides，other than后面时，如果这些介词之前有行为动词do (而非助动词)的各种形式。那么这些介词后的不定式不带to，否则带to。

She could do nothing but cry.

她除了哭别无办法。

I have no choice but to wait.