The contract is very important for both of you, so studying it________before signing is necessary.[ ]

A. in return  

B. in exchange

C. in detail  

D. in turn

下列单位中，属于建设工程竣工验收主体的是（）。

A.质量检测站 

B.项目咨询单位 

C.监理单位 

D.建设行政主管部门