题目内容:
The heating system of this building is much more cost-effective than that of the previous system _______ we used last year.
A.in where
B.where
C.in which
D.which
参考答案:
The heating system of this building is much more cost-effective than that of the previous system _______ we used last year.
A.in where
B.where
C.in which
D.which