单选题 My watch is nowhere to be found. I ______when I was on the bus.
A. must drop it B. might drop C. must have dropped it D. should have dropped it.

【正确答案】 C

【答案解析】[解析] 到处都找不到我的手表，我一定是在乘公交车的时候落下了。
[考点] 谓语动词
[解析] 选项A表示对现在的肯定推测；B选项表示可能性不大的推测：must have done表示对过去有把握的肯定推测；should have done表示过去本应该做……。