定语从句do you know the reason why he didn't come?why为什么可以用For which代替用which的话后面一定
问题描述：
定语从句do you know the reason why he didn't come?why为什么可以用For which代替用which的话后面一定
要缺成分,而用why后面则不缺成分.两者不矛盾了吗?
答
Do you know the reason why he didn't come?===Do you know the reason for which he didn't come?
语法：
the reason why==the reason for which