3.做宾补：

不定式可以表示一次性、具体性行为，以及将来意义的行为。现在分词可以表示当时正在发生的进行意义的行为，亦可表示-个持续时间的延续性的行为动作。过去分词可以表示完成意义的行为或状态，及物动词的过去分词亦有被动意义，不及物动词的过去分词仍是主动意义。

When I came in, I saw her dancing happily.

I often hear her sing songs in English in her room.

They had the lights burning all night long.

I saw Li Ping pass by and enter the next room just now.

The mother will have the doctor examine her son again.

Tomorrow I'll have my hair cut.

When I got home I found the window broken and the thief gone away already.

When they returned to their hometown, after an absence of twenty years, they found everything changed.

4.做表语：

不定式和动名词做表语解释主语内容，且可以和主语颠倒，意思仍然通顺，回答what的问题。它们有时存在经常性和一次性行为的区别，分词做表语表明主语的性质、特征和状态，不能和主语颠倒，可以回答how的问题。

Her job is cleaning offices.(What is her job?) (Cleaning offices is her job.)

Our job today is to clean the office.(=To clean the office is our job today.)

The news is very exciting.(How is the news?)

They are very tired after a long walk.

The door is locked now.

The children are well dressed these days.