— What did you say to Julia? I saw her crying in the dormitory alone.

— It _____ my fault. We talked happily when I was with her in the classroom.  [ ]

A. must have been

B. should have been

C. shouldn't have been

D. can't have been

双方均承担人工、材料、机械等要素的市场风险，属于( )。

A．固定单价合同

B．固定总价合同

C．可调价合同

D．成本加酬金合同