定语从句用which的八种情况分别是什么?

具体如下：

1. 引导非限制性定语从句时，通常要用which：The current, which is very rapid, makes the river dangerous. 水流湍急，使这条河很危险。

2. 直接放在介词后作宾语时，通常要用which：She may be late, in which case we ought to wait for her. 她可能晚到，那样我们就要等等她。

3. 当先行词是下列不定代词或被它们修饰时much, little, none, all, few, every(thing), any(thing), no(thing) 等时，通常用that：All that she lacked was training. 她缺的只是训练。

4. 当先行词有the very, the only, the same 等修饰时，通常用that：This is the only example that I know. 我知道的例子只有这一个。

5. 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：This is the best dictionary that I’ve ever used. 这是我用过的最好的词典。

6. 当关系代词在定语从句中用作表语时，通常用that：China is not the country (that) it was. 中国已不是过去的中国了。

7. 当先行词是一个既指人又指物的并列词组时，通常用that：They talked about the persons and things that most impressed them. 他们谈论了使他们印象最深的人和事。

8. 当要避免重复时：Which is the course that we are to take? 我们选哪门课程？

which的用法：

which

读音：英 [w?t?]? 美 [w?t?]。

释义：哪一个;哪一些。

which用作疑问代词时,在特殊疑问句中用作宾语或主语。

which用作关系代词,可引导限制性定语从句或非限制性定语从句,引导非限制性定语从句时which可以用整个主句作为其前行词,相当于and that,有时还可引导不定式短语从句。