位置 可位于主句之前、之中或之后 引导的从句不能位于主句之前 意义 常用来表示说话人对于某事的态度、解释或评论等，含有"正如......"的意思 一般表示某事的状况或结果 　　As is announced in today's newspaper, we must improve our style of work.

　　正如今天的报纸上说的，我们必须改进工作作风。(as引导非限制性定语从句，代指后句we must improve our style of work)

　　Taiwan, as we all know, belongs to China.

　　众所周知，台湾属于中国。(as引导非限制性定语从句，代指整句意思)

　　It rained hard yesterday, which prevented me from going to the park.

　　昨天雨下得很大，这阻止了我去公园。(which引导非限制性定语从句，代指前句It rained hard yesterday)

　　[点津]　as引导的定语从句，常用在一些固定结构中。

　　as is known to all　　　　　　　众所周知

　　as has been said before 如前所说

　　as is often the case 情况常常如此

　　as has been pointed out 正如已经指出的那样

　　as often happens 这种情况常常发生

　　即时演练2

　　选词填空：as, which

　　①As we had expected, Tom passed the driving test.

　　②Global warming, as we all know, has caused a lot of natural disasters.

　　③Tom passed the exam, which made his parents very happy.

　　④He said that he had never seen her before, which was not true.

语法点三 限制性定语从句和非限制性定语从句的比较 　　

限制性定语从句 非限制性定语从句 形式上 不用逗号和主句隔开 用逗号和主句隔开 意义上 是先行词不可缺少的定语，是对先行词的修饰限定，不能删去 是对先行词的补充说明，删去后意思仍完整 译法上 翻译成先行词的定语，"......的"

He is the man whose car was stolen.

他就是汽车被盗的那个人。 通常翻译成主句的并列句。

I've invited Jim, who lives in the next flat.

我邀请了吉姆，他就住在隔壁。