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题目内容
（郑州工程技术学院-大学英语（2）.）
31.
My wallet is nowhere to be found.I_____it when I was on the bus.
(A) must drop
(B) should have dropped
(C) had dropped
(D) must have dropped
My wallet is nowhere to be found.I_____it when I was on the bus.
(A) must drop
(B) should have dropped
(C) had dropped
(D) must have dropped
参考答案