IS THIS factory to which you paid a visit last week句中的 to wh

1.楼主的句子如果抄写完整的话,那么这就是一个错句.
正确的句子应该是：
Is this the factory to which you paid a visit last week?
而楼主的那个句子中的主句的be动词之后无表语,即没有先行词.
2.此时,我再回答楼主的这个问题：
不能,which不能换成that.
3.此句中的关系代词which代替先行词the factory,在定语从句中充当介词to的宾语,即构成固定短语：pay a visit to which = pay a visit to the factory.
4.而定语从句语法规定：如果关系代词做定语从句中介词的宾语,且该介词和关系代词一起提前至定语从句句首时,则指代人时用关系代词whom,而指代物时只能用which,不能用who和that.