1.作
谓语动词的成分,进行时,结构were/was/be+doing,例句:I am reading.She was running.
2.做非谓语,一般与主语构成主动关系,例句:There is a boy standing by the door.
3.引导
结果状语从句,一般为顺其自然的结果,例句:The strong flood struck the small town,causing a huge damege.
4.作
动名词充当主语或宾语,例句:Having fresh fruits and vagetables is of great importance for us to our healthy.
5.作形容词,通常意为"感到.......的“,例句:I think this book is very interesting to read.