2. 先行词（指物的）前面有only, few, one of, little, no, all, every, very等词修饰时
3. 先行词被序数词first, last, next等或形容词的最高级修饰时
4. 当先行词既有人又有物时
5. 当主句是以who, which或what开头的特殊疑问句时
关系副词
时间状语
when
Can you tell me the time 【when the film will start?】
I will never forget the day, 【when I joined the Party.】
地点状语
where
the waves soon carried me to an area 【where the other fishermen were. 】
This is the school 【where I studied a few years ago.】
Let’s go to the concert,【where you will find much fun.】
原因状语
why
the reason 【why I'm here to tell the story】 is that I made the right decision.
Do you know the reason 【why he is not here now?】
介词+关系代词
介词+which/whom
【例1】The man 【to whom you talk just now】 is a famous runner.
【例2】The service 【about which the students complain a lot】 should be improved.
【例3】He is a library assistant 【from whom I borrowed some books.】
【例4】It is a famous school 【from which he graduated 3 years ago.】
【例5】The chair 【on which he is sitting now】 is made of wood.
例句
【例1】This is the house 【where I lived two years ago.】
=This is the house 【in which I lived two years ago.】
【例2】Do you remember the day 【when you joined our club?】
=Do you remember the day 【on which you joined our club?】
【例3】I don’t know the reason 【why he said so.】
=I don’t know the reason 【for which he said so.】
非限定性定语从句
(1) His mother, who loves him very much, is strict with him.
(2) China, which was founded in 1949, is becoming more and more powerful.
引导词which和as
As和which都可以在定语从句中做主语或者宾语，代表前面整个句子。
(1) He married her, as/which was natural.
(2) He was honest, as/which we can see.
as引导非限制性定语从句，可放在主句之前，或者主句之后，甚至可以切割一个主句；which引导的非限制性定语从句只能放在主句之后。另外，as有“正如……，正像……”的意思
(1) As is known to all, China is a developing country.
(2) He is from the south, as we can see from his accent.
(3) John, as you know, is a famous writer.
(4) He has been to Paris more than several times, which I don't believe.
