单选题
My wallet is nowhere to be found. I ______ when I was on the bus.
A、
must have dropped it
B、
must drop it
C、
should have dropped it
D、
ought to have dropped it
【正确答案】
A
【答案解析】
情态动词。“must+have+过去分词”表示对过去发生的事情的推测。
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