We ______ last night, but we went to the concert instead.

A．must have studied

B．might study

C．should have studied

D．would study

世界各种事物之间的普遍联系是客观存在的，其中完全确定的关系是( )

A．函数关系
B．相关关系
C．回归关系
D．因果关系