定语从句中,关系副词可以互相转化.when=on+which.where=in+which .why=for+which.这是如何转化的?

关系副词和介词加关系代词之所以能转换,是因为它们的性质决定的.副词在句中可以做状语,介词短语也可以作状语.都在句中作状语这一特点是他们能转换的基础.
比如：He was born in that town.和 He was born there.两个句子都是说他出生的地方.其中
in that town = there .换成关系词就是 in which =where (其中的which 在原文中就是the town.
翻译：这就是他出生的那个城镇.
This is the townand he was born in the town.= This is the town in which he was born.(which=the town)
还可以这样翻译：This is the town and he was born there(there =in the town).=
This is the town where he was born(where 就是原句中的there).
why 和when 的转换和where的用法类似.只是why用来修饰reason,when 用来修饰时间名词.