Question

which是定语从句的关系代词，可不可以？

Answer 1

在定语从句中,which 和that 在指代事物时,一般可以互换使用,但并非在任何情况下都是这样,这里介绍宜用that, 而不宜用which 的情况.
①先行词为不定代词,all,much,something,everything,anything,nothing,none,the one等,
1.We should do all that is useful to the people .
2.There's nothing that can be said about it .
3.Do you mean the one that was bought yesterday?
②先行词被only, any, few, little, no, just, very, one of等词修饰时.
1.The only thing that we could do was to wait.
2.That's the very word that is wrongly used.
The last place (that) we visited was the chemical works.
You can take any (=whichever) seat that is free.
I hope the little that I can will be of some help to them.
比较 *This is one of the best novels that were published last year.
*This is the only one of the best novels that was published last year.
③先行词是序数词时或被序数词修饰时.
1.When we talk about Wuxi, the first that comes into mind is Tai Lake.
2.This is the third film that has been shown in our school this term.
④先行词是最高级或被最高级修饰时.
1.This is the best that can be done now.
2.The most important thing that should be done right now is how to stop him from going on.
⑤先行词既有人又有物,用which和who都不适合,这时宜用that. 如：
1.The writer and his novel that you have just talked about is really well known .
2.The rider and his bike that had run over an old woman were held up by the police.
⑥被修饰词为数词时.
1.Yesterday I caught two fish and put them in a basin of water .Now you can see the two that are still alive .
⑦如果有两个从句,其中一个关系代词已用which ,另一个关系代词宜用that,以避免语言的单调或重复.
Edison built up a factory which produced things that had never been seen before.
⑧疑问词是who或which,关系代词宜用that,以避免重复.
1. Which is the book that you like best?
2. Who is the man that is standing at the gate?
⑨主句是There be 结构,修饰其主句的定语从句宜用that 作关系代词. 如：
1. There is still a seat in the corner that is still free.
⑩被修饰成分为表语时,或者关系代词本身是定语从句的表语时,该关系代词宜用that .
1. That's a good book that will help you a lot.
2. My home village is no longer the place ( that ) it used to be .
定语从句中宜用which而不宜用that 的情况:
①当关系代词的前面有介词时.
1.A zoo is a park in which many kinds of animals are kept for exhibition.
2.Is this the room in which Mr. White lives?
②在非限制性定语从句中.
1.Crusoe's dog, which was are now very old, became ill and died .
2.More and more people are beginning to learn English, which is becoming very popular in our country. (which指代主句)
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 .
1. Let me show you the novel,that I borrowed from the library which was newly open to us.
2. At the station I bought some magazines that might help me to pass the time on the train and which I could pass on to others when I finished them.
④当关系代词后面带有插入语时.
1. Here's the English grammar which, as I have told you, will help improve your English.
⑤先行词本身是that, 宜用which .
What's that which she is looking at?
⑥先行词是those+复数名词.
A shop should keep a stock of those goods which sell best.

Answer 2

回答如下：
which不仅可以作关系代词引导定语从句，还可以作疑问代词引导特殊疑问句，还可以作连接代词引导名词从句(包括主语从句、宾语从句、表语从句、同位语从句)。例如：
This is the book which I bought yesterday.
I like the house which cost me lots of money.
Which class are you in?
Which is better, the red car or the white car?
I have no idea which class he is in.
I don't care about which of the books you will choose.
My question is which he wants.
Which city he will take a trip to has nothing to do with me.