II．关于on doing 作状语常见问题：

on prep.一......就......，后接v.-ing或表示动作的名词。

On seeing her，the king immediately falls in love with her. 一看见她，国王就爱上了她。

①On hearing the news，she burst into tears. 一听到这个消息，她就大声地哭了起来。

②On his return，he began to get down to his work. 他一回来，就开始工作了起来。

③On/upon his arrival at the airport，he was arrested by the police.他一到机场就被警察抓住了。

1. As soon as she saw it, the woman said she did not like it. =>Seeing it, the woman said she did not like it.

2. As soon as he opens the gate from the outside, he comes into the garden and waits until the gate shuts. =>On opening the gate from the outside, he comes into the garden and waits until the gate shuts.

3. The moment you leave this tent, you will get surprise. =>On leaving this tent, you will get surprise.

5. The tree was planted near the Church 50 years ago. It has gained an evil reputation only recent years. =>Planted near the Church 50 years ago, it has gained an evil reputation only recent years

Q1. 为什么1句用doing，2、3句用On+ doing呢？

Q2。为什么5句可以直接用被动式作状语，而4句用现在分词完成式的被动式做状语？

切记：on doing这个固定结构是表示"一....就...."，跟"as soon as"完全同一个意思！1也可以说成On seeing it, the woman said she did not like it. 除了2和3之外的句子考察的都是"分词表伴随"这个用法．注意，分词并不是简单的doing．其中，"伴随"就是伴随状态．是用现在分词还是过去分词，这取决于分词这个动作与主句主语的关系，是主谓关系就用现在分词，动宾关系就用过去分词．此外，分词的时态也要跟句子时态一致，这就是为什么4那里用了现在分词的完成时态，因为原句用了完成时态。

having done 和doing属于同一范畴，都是属于动词ing型，是非谓语动词。但是一般不会用来表结果，因为v-ing放句末就可以表结果了，为什么还要用having done 多此一举呢？ having done一般位于句首，做伴随或原因状语。因为有完成态在里面，所以这里面的动词的动作要与主句动词动作有一定时间的间隔。

如. Having finished my homework, I went out to visit Tom.

III．当堂练习:

（I）完成教材P18；P20~21 的练习。

（II）单选题

A. a policeman was asked to help 　　 B. the area was searched thoroughly

C. it was looked for everywhere　　 D. she hurried to a policeman for help

2. ________ such heavy pollution already, it may now be too late to clean up the river.