如果先行词（即被定语从句修饰的词）在从句中是主语或宾语，我们怎么选择that和which。which 引导定语从句时，先行词是物，在从句中可做主语、宾语、表语。that 引导定语从句时，先行词既可以是人+也可以是物，在从句中也可做主语、宾语、表语。更是在某些特定情况下，只能择一使用，要加强记忆。
一， 先行词是人，用that/who/whom引导从句；不能用which：
He that/who fears death lives not.
贪生怕死死的快。
A person that/who will swear, will lie.
开口就赌咒发誓的人往往在说谎。
I really admire people that/who speak two languages.
我真的很佩服会说两种语言的人。
（先行词在从句中做主语，用who/that）
There are always people (whom/who/that) you don’t get along with.
总有一些你没法相处好的人。
二，先行词是物，which和that都可以用：
She has a small office which is used for private discussions.
她有一间小办公室，用来私人会谈。
There is a kind of pleasure which/that comes from giving away.
付出带来一种快乐。
Anger is a wind which/that blows out the lamp of the mind.
愤怒是吹灭心灵之灯的风。
（愤怒使人丧失理智。）
三，先行词是代词，用that/who不用which：
Is there anything else that you'd like?
还再要点其他的吗?
God helps those who help themselves.
天道酬勤。
Money is something that most people will never stopping chasing.
大多数人永远不会停止追逐金钱。
There is nothing that can stop him from going there.
没有什么能阻止他去那儿。
You can accomplish all that you desire if you put your heart and soul in it.
如果你全身心投入，你就能实现你所渴望的一切。
当先行词是下列不定代词或被它们修饰时，比如much, little, none, all, few, every(thing), any(thing), no(thing) 等时，通常用that。
如：There was little that the enemy could do but surrender. 敌人无法,只有投降了。
You should hand in all that you have. 你应该把你所有的都交上来。
Do you have everything that you need? 你需要的东西都有了吗?
She would never do anything that was not approved of by her parents. 她父母不赞同的事她绝不会做。
但是如果他that为先行词，为了不重复用which:
What’s that which flashed in the sky just now?
刚刚天空闪过的是什么？
That which does not kill us makes us stronger.
那些杀不死我们的东西最终只会使我们变得更加强大。
Never deter till tomorrow that which you can do today.
今日事须今日毕，切勿拖延到明天。
四，先行词前有以下限定词，更多用that：
much, little, none, all, few, every, any, no；the very, the only, the same；形容词最高级或序数词
The best book that I read this year was 'The Da Vinci Code.'
我今年读的最好的书是《达芬奇密码》
The first thing that he noticed of her was her dark, long hair.
他首先注意到她的是一头又黑又长的头发。
They met the very afternoon that he spent in the library.
他们是在他在图书馆度过的那个下午认识的。
This is the only example that I know. 我知道的例子只有这一个。
The only thing that we can do is to give you some money. 我们能做的就是给你一些钱。
You are the very person that I am looking for. 原来你就是我要找的那个人。
So many traffic accidents that led to serious injuries are caused by drunk driving.
很多导致严重伤害的交通事故都是由酒驾造成的。
Parental love is the only love that is truly selfless, unconditional and forgiving.
父母的爱是唯一真正无私、无条件和宽容的爱。
The only thing that is worse than being blind is having sight but no vision.
唯一比失明更糟糕的是有眼无珠。
关于这一点，不能说用which就是错的！
五，可以用介词加which，不能用介词加that：
The tool with which he is working is called a plier. 他干活用的那个工具叫做钳子。
Mary may be late, in which case we ought to wait for her. 玛丽可能晚到，那样我们就要等等她。
The news report for which they were searching have been recovered. 他们找寻的新闻报道已找到了。
This morning some French wine came, for which I have to thank you. 今天早上送来一些法国红酒，为此我得向你道谢。
Your metabolic rate is the speed at which your body transforms food into energy.
新陈代谢的速度是你的身体将食物转化为能量的速度。
Behavior is a mirror in which everyone shows his image.
行为是一面镜子，每个人都把自己的形象显现于其中。
Experience is a school from which one can never graduate.
经验无止境。
Life is a flower of which love is the honey.
生命如花，而爱是它的蜜。
六，非限制性定语从句里，用which不用that：
She received a bunch of roses from her boyfriend, which came as a surprise. 她收到了男朋友的一束玫瑰花，这是她意想不到的。
She has to work on Sundays, which she doesn’t like. 她得在星期天工作，她是不喜欢这样的。
The Guangzhou team, which played so well last season, has done badly this season. 广州队上一个季度打得很好，这个季度却打得很差。
The wisdom of nations lies in their proverbs, which are brief and pithy.
民族之智慧蕴藏于其简短而有力的谚语中。
Unprofitable eloquence is like the cypress, which is great and tall, but bears no fruit.
夸夸其谈不济事，柏树参天不结果。
It's raining, which probably means that the football match will be cancelled.
下雨了，这可能意味着足球赛将被取消。
（which可以指代整个全句哦！）
八，如果先行词在从句中做宾语，that/who/whom/which都可以省略：
There are two points (which/that) I wanted to make.
我想说两点。
The cell is the unit (that/which) all living organisms are composed of.
细胞是构成所有生物的单位。
There are some things (that/which) you learn best in calm, and some in storm.
你会在风平浪静时学会一些事情，在暴风骤雨中学会另外一些。
总结如下：
在限制性定语从句中,只能用that不能用which：
1）当先行词是指物的不定代词例：
Do you have anything that you want to say for yourself?
2）当先行词前面有下列词修饰时：the only,the very,just,any,every,some等例：
This is the very busy that I’m waiting for.
3）当先行词有形容词最高级或序数词(包括last, next等)等修饰时，通常用that。
如：This is the best dictionary that I’ve ever used. 这是我用过的好的词典。
He is the last person that I want to see. 他是我不愿意见到的人。
The first thing that you should do is to work out a plan. 你应该做的第一件事是订个计划。
This is the best that has been used against pollution.
The train is the last that will go to Suzhou.
4）当关系代词在定语从句中用作表语时，通常用that。
如：South Africa is not the country (that) it was. 南非已不是过去的南非了。
5）当先行词既有人，又有物例：
They talked about the persons and things that most impressed them. 他们谈论了使他们印象深的人和事。
I won’t forget the things and the persons that I saw. 我不会忘记我看到的人和事。
Do you know the things and persons that they are talking about?
6）当主句的主语是疑问词 who 或 which 时例：
Which is the course that we are to take? 我们选哪门课程？
Which is the bike that you lost? 你丢失的自行车是哪辆？
Who is the woman that was praised at the meeting? 会上受到表扬的那位妇女是谁?
Which is the bike that you lost? Who is the boy that won the gold medal?
7）主句是there be句型且关系词在从句中作主语时例：
There is a seat in the corner that is still available.
当先行词指物，定语从句中只能用which不用that：
1）在非限制性定语从句中，只能用 which
2）当动词短语中的介词提前时，只能用 which
3）先行词后面有插入语时，只能用which.例：
Here is the English grammar book which,as I’ve told you,will help you improve your English.
4）先行词本身就是that时例：