There is no light or sound in the house．They must have gone to the cinema, ________?
A.didn't theyB.don't theyC.mustn't theyD.haven't they在线课程D
当must表示推测，作“一定，准是”讲时，反意疑问部分的动词形式要根据must后面的动词形式确定；但当句中有表示过去的时间状语时，反意疑问部分用didn't。