(1)当先行词为those，one，anyone，nobody等不定代词时。例如：

　　The one who knows me well is Tom.

　　(2)在分隔型定语从句中，先行词代指人时。例如：

　　A new master will come tomorrow who will teach you German.

　　(3)先行词为there be 结构的主语时。例如：

　　There is a man who wants to see you.

　　(4)当先行词是泛指代词he ,they或指示代词those等时，常用who或whom。例如：

　　We are badly in need of those who can work in real earnest.

　　(5)有两个定语从句出现在一个句子中，第一个关系代词用that的话，第二个应用who以免重复。

　　3.which/that区别:代指物时,一般可以互换,在下列情况下常选用that:

　　(1)先行词前有形容词最高级、序数词及all，every，no，some，any，little，much，the only，the very，the last等修饰词语时。例如：

　　I have read all the books that you gave me.

　　(2)先行词为all ,few ,nothing ,everything ,little ,much等不定代词时。例如：

He did all(that) he could to help us.

　　(3)先行词既表人又表物或者既表时间又表地点时。例如:

　　He talked about the teachers and the schools that he had visited.

　　(4)当主句主语是以who 或which 开头的疑问句时。例如:

　　Who is the man that called on you just now?

　　4.as引导限制性定语从句时，用于such(...)as,the same(...)as和as many/much...as结构中。例如：

　　Such book as you bought are useless.

　　5.关系代词在定语从句中作宾语时可以省略，但作主语时不可。

　　6.定语从句中关系代词作主语时谓语动词的单复数形式要与先行词保持一致。但是如先行词为复数名词且被the one of,the only one of,the very one of,the right one of或just the one of修饰时，定语从句中的谓语动词用单数形式。如果只是one of修饰，谓语动词用复数形式。例如：

　　He is one of those students who never finish work on time.

　　You have been the only one of the persons who has really influenced me.

　　二、关系副词

　　1.关系副词的一般用法列表如下:

关系副词 指代 先行词 所充当的成分 when 时间 时间名词 状语 where 地点 地点名词 状语 why 原因 reason 状语 We'll never forget the day when the People's Republic of China was founded.我们决不会忘记中华人民共和国诞生的那一天。

　　The office where he works is on the second floor.

　　他工作的办公室在二楼。

　　The reason why he didn't come was not made clear.

　　他没有来的原因没有表明。

2.时间名词、地点名词和reason后的定语从句中关系词如果充当状语则从句分别用when,where和why引导；如果是作主语或宾语，则用that或which引导其从句。例如：