什么时候用which

当关系代词在定语从句中作介词宾语时，我们通常用“介词＋关系代词”引导定语从句。如果指“人”，用“介词＋whom”；如果指“物”，用“介词＋which”。和别的形式的不同就是which或者whom作介词的宾语，而that等前面是不加介词的。

You must signal which way you are going to turn.

你要朝哪个方向转，必须发出信号。

There are two points which I wanted to make.

我想要指出的有两点。

We are still friends, though, which is good.

不过我们仍然是朋友，这令人感到欣慰。