i. 关系代词as, which引导修饰句子的定语从句
1. as, which引导非限制性定语从句，先行词可以是整个主句或主句的一部分。
China is in Asia, as is known to us all.
正如我们都知道的那样，中国在亚洲。
Light goes faster than sound , which is a fact.
光比声跑得快，这是事实。
He said he had been to America , which isn't true.
他说他去过美国，这并不真实。
2. as, which在从句中作主语时，其从句的谓语总是用第三人称单数形式。
They are invited to dinner, which makes them very happy.
他们被邀请去进餐，这使他们很高兴。
3. as意为“正如”，引导的从句可放主句前，但which引导的从句不能放主句前。
As we all know , China is a third world country.
正如我们都知道的那样，中国是个第三世界国家。
4. 从句是被动语态时，多用as引导从句。
China has sent up another man-made satellite, as was reported.
正如报道的那样，中国又发射了一颗人造卫星。
5. 从句谓语是know, see等时，一般用as引导从句。
This man, as you know , is good for nothing.
正如你所知道的那样，这个人一事无成。
6. as可用于the same ... as, such ... as结构中，但which不能：
We're facing the same problem as we did years ago.
我们正面临几年前面对的相同问题。
They're just such persons as we trust.
他们就是我们信任的这类人。
7. which=and that意为“这一点”，当从句是否定的，或者从句的谓语是系表结构，或者从句的宾语是复合结构时多用which引导从句。
They said they were from France, which wasn't true.
他们说他们来自法国，这并不真实。
Last night I dreamed a spirit, which kept me awake all the night.
昨天夜里我梦见鬼了，这使我一夜未眠。
8. as, which引导非限制性定语从句时，不仅可以在定语从句中作主语，也可以作宾语或表语，但是不能省略。
As you told me , he is always very kind to everyone he works with.
正如你告诉我的那样，他总是对一起工作的所有人都很和善。
He is a foreigner, which/as I know from his accent.
他是个外国人，这从他的口音我就知道。
He seemed a foreigner, as/which in fact he was.
他好像是个老外，其实他就是个老外。
专项练习
1. He must be from Africa, _______ can be seen from his skin.
A. that
B. as
C. it
D. what
2. They have decided to stay at home, _______ I think, _______ a wise choice.
A. which; are
B. which; is
C. that; are
D. that; is
3. William became the first American woman to win three Olympic gold medals in track, _______ made her mother very happy.
A. it
B. that
C. which
D. this
4. _______ everybody knows, he is very good at speaking English.
A. Which
B. That
C. Who
D. As
5. She heard a terrible noise, _______ brought her heart into her mouth.
A. it
B. which
C. this
D. that
6. The weather turned out to be very good, _______ was more than we could expect.
A. what
B. which
C. that
D. it
7. The number of the people present, _______ we had expected, was very large.
A. who
B. whom
C. that
D. as
8. That house, the doors _______ are painted white, is my grandpa's.
A. whose
B. which
C. of which
D. that
9. _______ has already been pointed out, grammar is not a set of dead rules.
A. As
B. It
C. That
D. Which
10. _______ is natural, he married Mary.
A. It
B. What
C. Which
D. As
答案速查 1-5 BBCDB 6—10 BDCAD
