定语从句中的that和which的用法
引导定语从句的关系代词有：that（指人或物）,which （指物）,who (指人）.指人时可用that或who ；指物时可用that 或which 。

That和which在从句里都可以做宾语和主语，做宾语时可以省略。

指物时，两者一般可以互换，但在下列情况下只能用that：
1）当先行词是all ,any ,anything ,everything ,nothing 或被它们修饰时.例如：
Is there anything that I can do for you
有什么可以为你做的吗?
All that can be done must be done .
凡是能做的都必须做.
2）当先行词被形容词的最高级或序数词修饰时.例如：That is one of the most interesting books that are sold in the bookshop .
那是这家书店出售的最有趣的书之一.
The first thing that we should do is to get some food .
我们该做的第一件事是弄点吃的.
3）当先行词有：the only ,the very ,the same ,the last 等修饰时.例如：
My necklace is not the only thing that's missing .
我的项链不仅是丢掉的东西.
4）当主句以who或which开头时,定语从句中引导词用that ,不用which 或who .以避免重复.例如：
Who is the girl that is wearing a red coat
正穿一件红色外套的女孩子是谁?
5）当先行词既有人又有物时,用that .例如：
The writer and his novel that you have just talked about are really well known .
你刚才谈起的那位作家以及他的小说确实很著名.
请注意: 以下几种只能使用which的情况:
1.引导非限制性定语从句，用which。

2.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。

3. 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.
2017.12.14。