也不是凡是先行词是时间都用when是地点都用where是原因都用why,得看这个词在从句中作什么成分.如Ineverforgettheday(which/that)Ispentinthevillage.IneverforgetthedaywhenIstayedwithyou.=Ineverforgettheday.OnthedayIstayedwithyou.=IneverforgetthedayonwhichIstayedwithyou.

　　至于关系副词一般可以用介词加关系代词替换,判断用哪个介词有两个原则：一,看先行词与介词的关系,如reason常与for搭配,theday与on搭配,二、看动词与先行词的关系.如ThemanwithwhomIgofishingisMrwang.具体的看看定语从句的相关语法解释