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

【正确答案】 C

【答案解析】[解析] 到处找不到我的表，我准是把它掉在公共汽车上了。“must+现在完成时”表示对过去的肯定推测。