there is no light in the dormory(宿舍).They must have gone to the lecture,___?A.didn't they B.haven't they答案是B可是为什么啊
问题描述：
there is no light in the dormory(宿舍).They must have gone to the lecture,___?A.didn't they B.haven't they答案是B可是为什么啊
答
宿舍里没有灯光,他们必定是去听讲座了,不是吗?
这儿的反意疑问句中must have done 是表推测判断的,have作助动词,类似于do 的用法,故用haven't they.类比They cannot have gone to the lecture,have they?（否定的推测与判断）