只用which不用that的情况引导非限制性图定语从句时、当关系词前有介词时、当关系代词后面有插入语时，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。
例句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。
