1．当先行词为everything, anything, nothing, all, none, few, little等词时，或当先行词被every, any, all, some, no, little, few, much等词修饰时。
Everything that they said was true.
他所说的一切都是真的。
He is dead and there's nothing that can be done.
他死了，再也没有什么办法了。
There was little that we could do to help her.
我们没有什么能帮助她的。
These walls are all that remain of the ancient city.
这些墙是这座古城所残存下来的全部。
提示：
something 后面可用which引导定语从句。
There is something(which/that) I'd like to tell you. 有些事我想告诉你。
2．介词后面。
关系代词紧跟在介词或短语介词后面，只能用which或whom，不能用that。
He climbed up to the top of a large rock, from which he got a good view.
他爬到一块巨大的岩石顶上，从那里他看到很好的景色。(也可用from where)
Sound is a tool, by means of which people communicate with each other.
声音是工具，人们通过这个工具进行交流。
They asked me a lot of questions, most of which I couldn't answer.
他们问了我许多问题，大部分我都不会回答。
C．只用that
在下列情况下，限制性定语从句中一般只用that引导
1．在非限制性定语从句中。
The weather was very terrible, which we hadn't expected.
天气非常糟糕，这我们没有料到。
4．先词与定语从句被其他词所分隔时。
Don't tell anyone about the secret who oughtn't to know.
不要把这秘密告诉任何一个不该知道它的人。
I was the only person in my office who was invited.
我是办公室里唯一受到邀请的人。
B． 只用which/whom
在下列情况下，一般不能用that代替which/whom。
3．在there here be开头的句子中。
Here is a boy who wants to see you.
有个男孩想见你。
2．先行词是one, anyone, those时。
One who has nothing to fear for himself dares to tell the truth.
一个无所畏惧的人敢说真话。
Anyone who breaks the law shall be published.
任何犯法的人都将受到惩罚。
Those who are against the plan put up your hands please.
凡是反对这项计划的人，请举手。
引导定语从句的关系代词和关系副词的选用，比较复杂除了牵涉到所指的先行词是人还是物，所引导的定语从句是限制性的还是非限制性的，以及关系词在从句中充当什么句子成份外，还要根据习惯用法而定。
A．只用who
在下列情况下，一般不能用that代替who。
1．在非限制定语从句中。
His mother, who loves him very much, is strict with him.
他妈妈十分地爱他，对他要求很严格。
3．当先行词是专有名词，或先行词本身指示意义十分明确时。
Mr. Joe lives in Beijing now, which is quite a long way from here.
乔先生现在住在北京，那里距离这儿很远。
I congratulate my neighbour, whose son has just won the election.
我祝贺我的邻居，他的儿子刚刚赢得选举。
2．当定语从句修饰整个主句时。
Taiwan belongs to China, as everyone knows.
众所周知，台湾属于中国的领土。
天气非常糟糕，这点们没有料到。
根据定语从句在句中所起的作用，可分为限制性定语从句和非限制性定语从句两大类。
A．限制性定语从句
限制性定语从句是先行词在意义上不可缺少的定语，用于修饰和限定先行词。如果去掉，主句的意思就不完整或失去意义。书写时不用逗号与先行词分开。
This is the boy who broke the window.
这就是打破窗子的孩子。(the boy是先行词，who broke the indow是限制性定语从句，明确指出the boy是打破窗子的那个孩子)
I have a book which teaches English grammar.
我有一本讲解英语语法的书。(a book是先行词，which teaches English grammar是限制性定语从句，修饰the book)
The people whom you met in the hall are from Japan.
你在大厅见到的那些人来自日本。(定语从句whom you met in the hall定先行词the people)
B．非限制性定语从句
非限制性定语从句在意义上只是一个附加修饰语，对先行词或主句作些附加的说明。如果去掉，主句的意思仍然清楚。书写时往往用逗号与先行词分开。
I, who am your friend, will share the work with you.
我是你的朋友，将与你分担这项工作。(I是先行词，who am your friend是非限制性定语从句，对先行词I起附加说明的作用)
New Concept English is intended for foreign students, which is known to us all.
新概念英语是专为外国学生编写的，这是我们大家都知道的。(which is known to us all是非限制性定语从句，对主句作进一步的补充说明)
C．在下列情况下，通常使用非限制性定语从句。
1．当先行词表示的是世界上独一无二的人或物时。
The sun, which gives us light and heat, is a fixed star.
太阳是一颗恒星，它给我们光和热。
Last year I visited the People's Great Hall, where many important meetings are held every year.
去年我参观了人民大会堂，每年许多重要会议都要在那里举行。