一
先行词指物的特殊情况：一． 必须用that的情况：
1.先行词被序数词、形容词的最高级修饰时,eg.This is the first job that I have taken up.
This is the most interesting novel that I have ever read.
2.先行词是不定代词,something somebody nothing anything 等 或是 all little much 时,
eg.There is something that I want to tell you.
3.先行词被all/ any/ every/ each/ few /little/ no/ some/ much/ only/ none/ both/ either/ neither 等修饰时,
eg.I have read all the books that you lent me.4.先行词被the only,the last,the very…修饰时,eg.This is the only method we can use.5.先行词又有人又有物时,
eg.They talked about things and persons that they know in the school.6.主句以who 或which开头时,
eg.Who is the old man that speak to you just now
二、修饰物时只用which不用that的情况 1,引导非限制性定语从句时.例如：
Bamboo is hollow,which makes it light.竹子是空心的,这使得他很轻.2,当关系词前有介词时.例如：
This is the room in which Chairman Mao once lived.这就是毛主席曾经住过的地方.
3,在一个句子中有两个定语从句,其中一个定语从句的关系代词用了that,另一个宜用which.例如：
Let me show you the novel that I borrowed from the library which was newly open to us.我来给你看我从新开的图书馆里借来的那本小说.4、当关系代词后面有插入语时.例如：
Here is the English grammar which,as I have told you,will help improve your English.这就是我跟你说过的会有助于你学好英语的那本英语语法书.5、先行词为that时.例如：
The clock is that which can tell us the time.钟是报时的装置.
三、修饰人时只用who不用that的情况
1、先行词为one,ones,anyone,those指代人时.如：
The person I want to learn from is one who studies hard and works well.我最羡慕的是学习勤奋,工作出色的人.2、在There be结构中,修饰主语的定语从句宜用who关系代词指代人.例如：
There’s a gentleman who wants to see you.有位先生想见你.3、当先行词有较长的后置定语时.例如：
I met a foreigner in the park yesterday afternoon
who could speak Chinese very well.昨天下午我在公园里遇到一位中文讲得非常好的外国人.
4、一个句子中带有两个定语从句,其中一个定语从句的关系代词是that,另一个宜用who以避免重复.例如：
The student that was praised at yesterday’s meeting is the monitor who is very modest and works very hard.受到校长表扬的学生是位谦虚好学的班长.
四．先行词为the reason时,分析后面的定语从句,如果定语从句缺乏主语或者宾语或者表语,先行词用关系代词that/which,做宾语可以省略；如果从句完整,不缺主语或者宾语或者表语,先行词用关系副词why.例如：1.I don't believe the reason ______ you give me.2.I don't know the reason ________ he is late.
分析：例1定语从句是______ you give me,give 为及物动词,缺宾语,所以要填关系代词that/which/省略； 例2定语从句为________ he is late,从句完整,填关系副词why.
掌握一个句型：the reason why~is that~
例如：The reason why he is late is that he got up late.因为why he is late是定语从句,that he got up late是表语从句.
