关系代词which在定语从句中通常只用于指事物，不用于指人。它在句子中主要用作主语或宾语。如：
She was not on the train which arrived just now. 她不在刚才到达的那列火车上。(which在定语从句中用作主语)
I’ve found the car keys which you were looking for. 你要找的汽车钥匙我找着了。(which在定语从句中用作宾语)
关系代词which有时还可在定语从句中用作定语。如：
He advised me to hide behind the door, which advice I took at once. 他劝我躲在门后，我立即照他的话做了。
注意，关系代词which原则上只指物，不指人。但是，有时指的不是具体的某人，而是指某人的职业、身份、地位、职务、品质、特征等，此时要用which 而不用who。如：
He talked like a scholar, which he was not. 他说起话来像个学者，其实他没什么学问。
She talked like a native, which she hardly was. 她说起话来像是个本地人，其实她不见得是。
They accused him of being a traitor, which he was. 他们指控他是叛徒，他真是叛徒
