当主语：e.g.1、To buy this book took me 100 yuan.
2、Running is good for your health.
★注：不定式当主语时常放到句子后面去，而在原来的位置以形式主语 it 来代替。
e.g. To buy this bike took me 100 yuan.——→It took me 100 yuan to buy this book .
当宾语(常考)：e.g.3、They decided to buy a new TV. 4、We enjoy talking in English.
当表语：e.g.5、My work is to feed the animals .
当定语：e.g.6、Have you got something to eat ?
Do you know the crying boy ?( 动名词当定语)
当状语：e.g.7、 I must go home to get some more money . （目的状语）
8、The man's cutting the big tree (by) using a long knife（方式状语）(by常省略)
当补语(常考)：e.g. 9、Mr Wei asked me to go with him .10、 Did you make the boy laugh ?
