定语从句中关系代词一般由Who或which引导，属性为人或者拟人用Who属性为物用which。那花样的定语从句，则是大道归一，推理过程。
When 用法推理
1、我都悉芹嗤谚忘记你过来的日子了。<1>分我忘记日子了。你在那个日子来的。<2>合I have forgot the day you came on the day.I have forgot the day on which you came.I have forgot the day when you came则关于时间的定语从句，如有“介词+which”可以用“when”代替，时间不等于when，必须“介词+which”。
Why 用法推理
1、我不理解他离开我的原因。<1>分我不理解原因。他因为这原因离开我。<2>合I don’t understand the reason he left 罪焐芡拂me for the reason.I don’t understandthe reasonhe left me forwhich.因Why可以描述原因，则句子变为I don’t understandthe reasonhe left me why.
