2、当先仃词被the only,the very,any,few, little,no,all修饰时。 例：All the books that you offered has been given out.
3、当先行词是形容词最咼级或先行词的前面有形容词的最咼级修饰时。 例：This is the best book that I have ever read.
例：I like the person to whom the teacher is talking.
1、Such+名词+as…像…一样的，像 …之类的…例：Don' t read such books as you can't understand.
3.先行词本身是that时，关系词用which,先行词为those, one, he时多 用who。
6、当主句的主语是疑冋词who、which时。 例：Who is the man that is making a speech?
7、有两个定语从句时，其中一个用了which另外一个宜用that。
例：Edis on built up a factory which produced things that had n ever bee n see n before
3、…such…as…。such代词"这样的人或物”as在从句中修饰such
例：
【区别】
1、引导的非限制性定语 从句只能放在主句后。
例：
例：
2、当定语从句放在主句 后面时并不是as就永远
等于which
⑴当非限制性定语从句是否定句或表示否定意义时。只用which。 例：
⑴as仍然保持做连词的某种意义
例：
例：Those who respect others are usually respected by others.
2、the same+名词+as… 和冋样的
例：
4.当关系代词后面带有插入语时
例：Here is the English grammar which, as have told you, will help improve your En glish.
⑵从句中行为动词是主动语态，一般用which做主语。例：
⑵当as在从句中做主语时，后面常接动词的被动语态。(be know,be said)
例：
⑶当非限制性定语从句的 谓语动词是一个复合结构时 ，只能用which。例：
⑶as常用在as(it)same likely, as(it)often happens, as(it)was point out As(it)was said earlier, as I remember(it),as I understand(it),as(it)Appears
例：He worked hard the whole time (when/that) he lived here.
October 1, 1949was the day when/that the People's Republic of China was founded.
只用which, who, whom的 情况
用于限制性定语从句
非限制性定语从句关系代词与关系副词的用法：
指人
指物
既指人又指物
1关系代词和关系代词在任何条件下都不能省略。
主格词
Who不可省
Which
That不可省
2、Who whom which不能用that代替也不能相互替换。
宾格词
Who（m）可省丁
3、在“介词+Which/Whom”从句的结构中介词不能移到从句后面。
8当先行词在主句中作表语，而关系代词在从句中作表语时。 例:China is not the country that it was.
9、当要避免与疑问词which重复时
例:Which is the car that was made in Beijing?
10.主句是There be结构，修饰物，充当主语的定语从句宜用that作关系代词。（备注：在There be结构中，修饰人，充当
4、当先行词是序数词或前面有序数词修饰时。
例：We talked about the persons and things that we remembered.
5、当先行词即有人又有物时。
例：They talked about the teachers and the schools that they knew.
主语的定语从句宜用关系代词who指代人
例:There's still a seat in the cornthat is still free. There's a gentleman who wants to see you.
11、that有时可用来代替when,引导一个疋语从句，修饰表示时间的名词如day, time, moment等。
属格词
Whose/of whom不可省
Whose/of which不可省
Whose不可省
4、when where可以用于非限制定语从句中。
、关系代词用法
That
（限制定语从句中必须用 的几种情况）
1、当先行词是不疋代词all,much，little，something everything, anything, nothing, none, the one时。 例：He told me everything that he knows.
定语从句
【区别】限制性定语从句 对先行词起修饰作用（相当于形容词的作用，他的作用一是放在先行词与定语从句中间起了连接作用，二是在从句中担当一个成分，并与先行词保 持数的一致。） 非限制性定语从句 对先行词起补充说明作用，先行词与定语从句往往用逗号隔开，句子相当于并列句，状语从句。
一、关系代词分类
用于限制性和非限制性定语从句
1.在非限制性定语从句中，只能用which指代物，用who/whom指人
例：He has a son, who has gone abroad for further study
As(即可以引导限制定语从句又可以引导非限制介词+关系代词”引导的定语从句中，只能用which指物，whom指人。