5.当定语从句位于主句之后，纯粹表示主句所述的内容，不带有“如……那样”的意思时，往往用which, 而不用as。例如：

They were invited to the state banquet, which(as) was a great honor to them.他们被邀请参加国宴，这对他们来说是莫大的荣幸。

We had to sleep in our wet clothes, which was most uncomfortable.我们不得不穿着湿衣服睡觉，这简直太不舒服了。

Mummy always treats me just like a baby, which I can’t bear.妈妈老把我当成小孩子对待，这让我无法忍受。

4.做主语时，which既可以作系动词be的主语，也可以作实义动词的主语，而这时as 只可以做系动词be的主语。例如:

He married her, which was natural.(可用as代替which)他和她结婚，这是很自然的事。

He won a /the Nobel Prize in chemistry, which made him illustrious(不可用as代替which)他获得了诺贝尔化学奖，这使他名扬天下。

3.当which引导的从句在意义上近乎并列关系时，可以用and this, and that代替，意思是“这件事”，例如：

He changed his mind, which(and this, and that) made me very angry.他改变了主意，这使我很生气。

She has married again, which(and this, and that ) was unexpected.出乎意料的是，也又结婚了。

而as主要起与上下文连接的作用，表达说话人的看法、观点，并指出主句内容的出处或根据等，例如：

Einstein, as we know, is famous scientist.爱因斯坦，众所周知，是位伟大的科学家。

As is announced in today’s newspaper, we must improve our style of work.今天的报纸上说，我们必须改进工作作风。

2.在which引导的定语从句中，谓语动词若是am , is ,are则这些系动词不能省略，而as后面若是这种情况，则可以省略。例如：

He is a teacher, as (is) clear from his manner.(is可以省略)

He said he had never seen her before, which was not true.(was 不可省略)

1.which只能放在主句后面，而as引导的从句位置相对较灵活，可在前，可在后。例如：

As he realized, I was very useful to him.(在前)

Air, as we know, is a gas.　(在中)

He was a foreigner, as I know from his accent.(在后)

He came late again, which made his boss angry.(在后)

19. A. liberal education　　　　 　　 　B. group discussion 　　 　C. education　　　　　　　 　　　 　D. teaching

18. A. effect　　 　B. result　　 　　C. power　　 　 　D. end

17. A. easy　　　 　B. hard　　　 　　 C. possible　 　 D. proper

16. A. reasonable　 　B. remarkable 　　C. strict　　 　D. small

15. A. pulled　　 　B. pushed　　 　　 C. permitted 　 D. protected