两道结构一样的语法题,求赐教.that is the school----last year.This was the

两道结构一样的语法题,求赐教.that is the school____last year.This was the place __last year
that is the school___last year.
A.which I studied.B.at which I studied.C.where I studied.D.in where I studied
This was the place ___last year.
A.which I visited.B.where I visited.C.when I visited.D.in which I visited
为什么第一题选b第二题选a