Is this factory( )you visited last week?A.that B.where C.the

像这种含有定语从句的疑问句,最好的方法就是把它还原成称述句看看.
This factory is ( ) you visited last week?
现在就很明显了,此句缺少一个先行词,所以须填入the one/factory,关系代词代替the one/factory在定语从句中充当visited的宾语,所以关系代词可以省略,但先行词是不能省略的.
如果有人认为This factory不是先行词吗?那么这句的is后面就没有表语了.
再举个另一个句子:
Is this the factory ( ) you visited last week?A.that B.where C.the one D.in which
"木有道理不知道",can you tell me the answer?