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I didn't hear anything last night. I ( ) asleep.
A、could have been
B、must have been
C、might be
D、must be
【正确答案】：B
【题目解析】：must have been 对过去的肯定猜测； could have been 对过去的虚拟，本该做，实际没做；might be/must be 对现在的猜测，句子含义是我昨晚什么也没有听到，我一定是睡着了。