帮忙分析两个句字Qingdao is a beautiful city ,(to which )I pay a six-

帮忙分析两个句字
Qingdao is a beautiful city ,(to which )I pay a six-day visit.
这是一个定语从句,which是关系代词.在定语从句中介词+关系代词(即to which )不就等于关系副词where吗?为什么在这个句子中不能将to which换成where (这原本是道选择题)[A.which B.where C.in which D.to which
还有一道相似的题,This is the town( )I pay a visit to last year .备选答案为A.that B.which C.to which D.where 这又该选什么呢?