Question

You'd better hurry．Your friends________for you．

1. A.
   must have waited
2. B.
   must be waiting
3. C.
   must have been waited
4. D.
   must wait

Answer 1

B
分析：句意是“你最好要快点，你的朋友一定在等你。”四个选项中都有must．wait是个有进行时的行为动词，按句意时间是指现在。所以应该用B项must be waiting．must have waited是指过去时间。must have been waited指过去时间，是被动语态形式。must wait不表示“可能性”，而表示“必须”。