定语从句，求教

that在任何情况下都不可以和when,where,why互换,因为前者为关系代词,后者为关系副词
when,where,why=介词+which,介词+which一定可以换成when,where,why,但when,where,why不一定能换成介词+which,他们要互换,必须介词对
例如:we will never forget the days (when)we go to school together,因为有固定搭配 on the day ,所以when,可以用on which 换,但如果介词不是on,而是其他的如in /at +which就不对了
明白了吗?
总的来说,1在定语从句中,that在任何情况下都不可以和when,where,why互换
2when,where,why=介词+which,如果题目可以用
介词+which,就一定能用when,where,why,但能用when,where,why,不一定可以用介词+which(必须介词的搭配正确)