航班延误或取消时，承运人应迅速及时将航班延误或取消等信息通知旅客，做好解释工作。
参考答案：对
----- Mary looks very upset. She _______ failed to pass the exam.
----- I guess so. It's very difficult after all.
A must have B could have C should have D might have
读下面的等高线地形图，完成要求。
E城为重化学工业城市，该城工业布局的有利条件有（），此山区要建一疗养院，甲、乙两地选址，以（）较好，理由是（）
