关系副词when, where, why,how的含义相当于"介词+ which"结构,因此常常和"介词+ which"结构交替使用,例如：
There are occasions when (on which) one must yield.
Beijing is the place where (in which) I was born.
Is this the reason why (for which) he refused our offer?
I’m surprised the way how (by which) he works out the problem