这里应该填needn't they?
下面是一些含有must句子的反义疑问句的情况
陈述句含有情态动词must有两种情况：
must表示“必须”,反意疑问句部分为mustn’t…?/ needn’t…?
He must study hard at English,mustn’t he?/ needn’t he?
You must go home now,needn’t you?/ mustn’t you?
We mustn’t be late,must we
Must表示推测：“一定,肯定” 反意疑问句部分与must后面的动词呼应
You must be joking,aren’t you?
He must be ill,isn’t he
注意：用must对过去的动作推测时,反意疑问句部分的助动词用did或have,而对过去的状态推测,反意疑问句部分的be动词用was:
She must have finished her work,hasn’t she / didn’t she
Jack must have arrived here yesterday,didn’t he
He must have been a policeman,wasn’t he
