—Could you tell us _________ to do it?

—Of course. First of all, you should clean the wall, then clean the floor.

A．when

B．what

C．how

D．whether

关节脱位是指

A．关节分离

B．关节面失去正常对合关系

C．关节囊扭伤并断裂

D．关节出现畸形和弹性固定

E．关节韧带断裂