---I knew she was in because I heard her radio, but she didn't open the door for me .---She ________ the bell.A.may not hearB.mustn't have heardC.may not have heardD.mustn't hear
网友回答
C解析考查否定推测的用法。
从题干中所提供的时态看这是一个对过去去发生的事情的推测。对过发生的事情的推测把握较大时用must + have +过去分词。由此我们首先排除A．D两项。但是must在用于推测时只能用于肯定形式，其否定形式必须用can't。
说明：表示推测疑问句要用can/could如：
Could the bank have made a mistake?
银行会不会出差错呢？
Where could he have gone on such a night?
在这样一个晚上他能到哪里去呢？
We couldn't have heard them because of the noise from the river.
由于江水的响声，我们不可能听到那声音。