which 限制性定语从句
This is the house in which you lived three years ago.
=This is the house where you lived three years ago.
定语从句有限制性和非限制性两种.限制性定语从句是先行词不可缺少的部分,去掉它主句意思往往不明确；非限制性定语从句是先行词的附加说明,去掉了也不会影响主句的意思,它与主句之间通常用逗号分开
that和which在定语从句中只能作主语或宾语,而where在定语从句中只能作地点状语.that和which的相同之处：都可以作主语或宾语,都可以指代人或物.that和which的区别：that的三不用：1、非限制性定语从句只能用which引导,不能用that引导.2、紧跟在介词后面的关系代词不能是that.如：Give me a pen with which I will write an essay.3、关系代词后面有插入语时不能用that.如：Here is the gramma book which,as I have told you,will help you improve your English.比较：Here is the gramma book which/that will help you improve your English.that的六必用：1、先行词有形容词的最高级修饰,或有序数词修饰时,必用that.2、在不定代词,如：anything,nothing,the one,all,much,few,any,little等作先行词时,只用that,不用which.3、先行词既有人,又有物时,只用that,不用which.4、在there be 句型中,只用that,不用which.5、先行词有the only,the very修饰时,只用that.6、 关系代词在从句中作表语并带有类比含义时,通常只用that,不用which.例如：He is no longer the star that he was.他不再是过去的那位明星了.