—Theyaresupposedtoarriveatsix,butthereisnosignofthem.—S...

问题详情：

—They are supposed to arrive at six, but there is no sign of them.

—Something unexpected          to them.

A．might happen                                                  B．must have happened

C．would have happened                                    D．could happen

【回答】

B

知识点：虚拟语气

题型：选择题