英语定语从句中as 怎么用（as代表前面的整个主句并在从句中作主语时,从句中的谓语必须是系动词；若为行为动词,则从句中的关系代词只能用which..） 这句话 我不懂啊 什么个意思啊?能不能给我讲明白了 然后举个例子?主要是后面的一句话，能不能举个例子啊？

As的用法：你所不能理解的那句话在下面也有详细的解释（见【 】中）,即是叙述了as与which的用法区别,也有例子,只不过叙述不同
一、as引导限制性定语从句
主要结构有：
the same…as
as…as
such…as
so…as
主句中出现the same, as, such, so修饰先行词,需选择as做关系代词在定语从句中做主语或宾语.
1. It’s the same person as we wanted to find yesterday .
我们昨天要找的是同一个人.
2. Such girls as he knows are good at English .
他所认识的女孩都擅长英语.
3. Do you have such books as we like ?
你有我们喜欢那种书吗?
4. She will marry as healthy a man as she can find .
她将嫁给她能找到的任何一个有钱人.
5. There is so warm a house as we want to live in .
这里有如此暖和的房子,我们都想住在里面.
6. He has so difficult a problem , as none of us can solve .
他有如此难的一个问题,我们没有人能解决.
二、引导非限制性定语从句
⑴ as引导非限制性定语从句,指代整个主句内容,从句可置于句首,句中或句尾
1． As everyone knows ,China is a beautiful country with a long history .
每个人都知道,中国是一个有着悠久历史的美丽国家.
2． The earth , as we know , moves round the sun .
地球,我们都知道,围着太阳转.
3． Tom works hard and is willing to help others, as we all know.
汤母工作努力,并且乐于助人,这一点我们都知道.
⑵ 非限制性定语从句中的谓语为被动式时,常用as做主语
be said/known/announced/reported/mentioned/expected/discussed
1. Grammar , as has been said before, is not a set of dead rules.
语法,就像以前所说,不是一套死规则.
2. As is known to all , * is part of China .
⑶ as引导非限制性定语从句,有“如,似,正像”的含义,因此,下列句式多用as
as has been said above
如上所说
as anybody can see
正像每个人所看到的那样
as we had expected
正如我们所预料的那样
1. Things are not always as they appear.
事情并不一直像他们表面那样.
2. The boy has as much progress as we had expected.
正像我们所预料的那样,这个男孩取得了大的进步.
【由as, which 引导的非限定性定语从句,as和which可代整个主句,相当于and this或and that.As一般放在句首,which在句中.
As we know, smoking is harmful to one';s health.
The sun heats the earth, which is very important to us.
as 和which在引导非限制性定语从句时,这两个关系代词都指主句所表达的整个意思,且在定语从句中都可以作主语和宾语.但不同之处主要有两点：
(1） as 引导的定语从句可置于句首,而which不可.
(2） as 代表前面的整个主句并在从句中作主语时,从句中的谓语必须是系动词；若为行为动词,则从句中的关系代词只能用which.. 】