1. 动词宾语的补足语，如：
　　The doctor warned me not to smoke and drink.

　　在表示感觉的动词如see, look at, watch, hear, listen to, feel, notice等，以及在使役动
　　词如make, have, let后的宾语补足语要省略to; help和find后的可省也可不省to，如：
　　I saw him enter the store.
　　He helped me (to) move the chairs.

2. 介词宾语的补足语，如：
　　It is right for them to leave now.
　　It was kind of you to help us.
　　He shouted to them to stop arguing.

3. 主语的补足语，如：
　　Everybody is expected to do his duty.
　　John was appointed to be in charge of the sales department.
　　主语补足语的to不省略，如：
　　Mary's father was seen to return after dark.
　　I was made to feel at ease