去分词, 表示该被动动作发生在位于动作之前.

She was glad to have been given so much help.

　　语法延伸:

一. 不定式的主动形式表示被动意义的情况

1. 不定式的主动形式表示所修饰的名词或代词构成逻辑上的动宾关系, 但是不定式的逻辑主语也在句子中出现时.

I have a letter to send today.

Do you have anything to say?

2. 在"There be + 名词 + to do"结构中, 不定式和句子中的主语构成逻辑上的动宾关系时, 如果强调的是必须有人完成某事时, 不定式多用主动形式; 如果强调的是事情本身必须被完成时, 则用被动形式.

There are many pigs to feed.

Are there any more letters to be typed?

There are a lot of homework to do / to be done.

3. 在"名词 / 代词 + be + adj. + to do"结构中. 常常用的形容词有easy, difficult, hard, impossible, nice, pleasant, light, heavy, interesting, important, expensive, cheap, fit, dangerous等.

He is hard to convince.

This problem is easy to work out.

4. 在"too....to do; enough.....to...."结构中.

The problem is too difficult to work out

The house is big enough to live in.

5. 在"with + 名词 + to do" 结构中.

With nothing to do, he lay in bed.

6. 当不定式含有在for sb. to do结构中.

This is the best book to read (= for us / you to read).

The important thing to do is to lock the door when we leave the house.

7. 一些作表语用的不定式的主动形式表示被动含义, 常见的这类词有: let(出租)，rent， hire， blame等.

The house is to let.