我这里有几道题目,答案已经有了,但是不知道这么做的原因,请大家回答我,

我这里有几道题目,答案已经有了,但是不知道这么做的原因,请大家回答我,
1、We have two spare rooms downstairs,_______________has been used for more than two months.
A.but neither of which
B.none of which
C.but neither of them
D.none of them
C 为什么A不可以）
2、Is thia book_________you wantted to borry last time?
A.which
B.that
C.the one
D.then
C 请你帮我四个选项都分析一下）
3、The other day,he showed me the house_______he was born.
A.which
B.whom
C.in where
D.in that
B 为什么这里不能用C）
4、We're going to visit a factory ______the Buick cars are made.
A.which
B.where
C./
D.in that
B 请你帮我四个选项都分析一下）
5、It was in the classroom_______we have Economics classes________I found my cell phone.
A.Where.where
B.where...that
C.that .where
D.that...that
B 请你帮我四个选项都分析一下）
回答的详细一点，帮我仔细分析下，