1)在非限制性定语从句中， which 可以代表主句的一部分，甚至全部，而不仅仅限于一个名词或代词：

He said he had never seen her before, which was not true.

他说他以前从未见过她，这不是真的。

He invited us to dinner, which was very kind of him.

他请我们去吃饭，这是他难得的好意。

We had to sleep in our wet clothes, which was most uncomfortable.

我们不得不穿着湿衣服睡，这很不舒服。

This I did at nine o’clock, after which (=doing it) I sat some time reading the paper.

我九点钟做了这事，之后我就坐着看了一会儿报。

2)which有时在从句中作定语：

He advised me to hide behind the door, which advice I took at once.

他让我躲在门后，我立即照着做了。

He believes in the abolition of capital punishment, which idea I am quite opposed to.

他主张废除死刑，对这种观念我是完全反对的。

She may not be in, in which case you could leave her a note.

她可能不在家，如果是那样你可以给她留个条。

He studied computer science, which knowledge is very important today.

他学的是电脑，这门知识现在很重要。

在书面语中，有时把这类从句单列成一句：

From which he learned a few lessons which were later of value to him.

从中他得到了一些教训，对他后来很有用处。

3)which还可以和不定式一起用：

Allow me one minute in which to change my costume.

给我一点时间去换装。

She had a little money in the bank, with which to help her mother.

她在银行存了一些钱，用这钱来帮助她的母亲。

Now he had no pretext on which to stay in the house.

现在他没有什么借口再这家待下去了。

4)which 有时还可以表示“任何一个”，意思和whichever差不多：

You may have which apple you like. 你想要哪个苹果就拿哪个。

Take which dresses you want from my wardrobe. 想要什么衣服就从我的衣柜里拿。

You may select which you like. 你可挑选任何你喜欢的。

Use which method you prefer. 你愿意用什么方法都行。