关系代词which在定语从句中一般用作主语或宾语，有时也用作定语，但前面一般有介词。如：
He won’t want to eat it unless he’s really hungry, in which case he’ll eat almost anything. 除非非常饿，不然他不会吃东西，一旦饿了他几乎什么都吃。
She may have missed the train, in which case she won’t arrive for another hour. 她可能没赶上火车，如果那样的话她还要过一个小时才能到。
假如前面没介词呢？which也可用作定语吗？谢谢！
假如前面没介词，which 也可用作定语，但在现代英语中极为少见。
依据柯林斯英语语法系列的《限定词及数目词》：在一些古老的文本里，可发现不带介词、修饰句子的which用作限定词的状况。但这种使用方法在现代英语中极为罕见。如：
He then resolved to leave, which decision pleased me greatly. 他那时决定离开，这个决定令我异常开心。
其他例句如：
We told him to consult the doctor, which advice he took. 大家叫他去看大夫，他听取了大家的劝告。
He is studying economics, which knowledge is very important today. 他学经济学，这种常识如今非常重要。
He believes in public ownership, which idea Im quite opposed to. 他相信公有制，这个思想我完全反对。
He advised me to hide behind the door, which advice I took at once. 劝我躲在门后，我立即照他的话做了。
