定语从句中的which
只能使用which的情况:
1. 在“介词＋关系代词”结构中，关系代词必须用which。
如： The house in which we live is very large. 我们住的房子非常大。
This is the reference book of which the teacher is speaking. 这就是老师正在谈及的那本参考书。
注意： 如果介词不放在修饰事物的限定性定语从句的句首， which就可换为that， 例如： This is the question which/that we've had so much discussion about. =This is the question about which we've had so much discussion. 这就是我们已经多次讨论过的问题。
2. 先行词为“those＋表事物的复数名词”时， 关系代词通常只用which而不用that。
如：you should grasp well those skills which may be used in the future work.
最后，记得这个特殊情况吧：当先行词是表示原因或方式的名词时，可以用that引导定语从句，相当于介词+which，that可以省略。
如： She likes the child for the very reason that (=for which) she loves his father. 她喜欢那个孩子因为她爱着孩子的父亲。
He didn't like the way that (=in which) she speaks to his mother. 他不喜欢她对他的母亲那样说话。
Imagine the speed that (=at which) he drives the car. 很难想象，他开车开得那么快。
The reason (that /for which /why) he came here was to ask for our help.他来这里的原因是寻求我们的`帮助。
which和that的区别：
1只用which,不用that的情况。
1)which可用在非限制性定语从句中。例如：
The project,which lasted four years,cost one billion dollars.这项工程历时四年，耗资十亿美元。
2)which可用前置介词宾语。例如：
This is the house in which we lived three years ago.这是我们三年前住过的那所房子。
2只用that，不用which的情况。
1)that相当于关系副词when,where,why,in the way＝in which。例如：
I'll never forget the Monday that /when you first arrived.我将永远不会忘记你初到的那个星期一！
Do you know anywhere that I can get fruit?
你知道我能在哪里买到水果吗？
I like the place for the very reason that/why you dislike it.我喜欢那地方的原因，恰恰是你不喜欢它的原因。
He doesn't see things the way that /in which we see them.他看问题跟我们不一样。
2)that既可指物，也可指人。例如：
The people that worked on the project made a good effort.从事那项工程的人们做了很大努力。
3)当主句以here,there开头时，常用that。例如：
Here is the place that you've been looking for.这就是你一直找的地方。
4)当先行词是序数词、形容词最高级或先行词被序数词或形容词最高级修饰时，常用that。例如：
The first(thing)that should bed one is to get the book.应该做的第一件事是弄到那本书。
This is the best place that I've ever visit-ed.这是我曾参观过的最好的地方。
5)当先行词是all,anything,nothing(something除外),none,little,much时，常用that。例如：
Is this all that's left?这就是剩下的所有东西吗？
Have you got anything that belongs tome?你有没有拿过属于我的东西？
6)当先行词被no,little,only,very,the last等修饰时，常用that。例如：
The only thing that could be done is to find
our way home.唯一能做的事情就是要找到回家的路。
7)当先行词是两个或两个以上的词分别表示人和物时用that。例如：
They talked about the teachers and the schools that they knew.他们谈到了他们熟悉的老师和学校。
8)在以which，who开头的句子中常用that。例如：
Which is the car that killed the man?撞死那个男子的小车是哪一辆？
9)time是先行词时，前面如有序数词或last修饰时，定语从句只能用that引导或省略。例如：
This is the last time(that)I shall give you a letter.
The first time(that)I saw him was last year.
