问题补充：
--- Tom , why didn’t you answer my call yesterday afternoon?
--- Sorry , I didn hear the phone . I asleep.
A. must be
B. must have been
C. could be
D. should have been
答案：
A. must be
(答案→)B. must have been
C. could be
D. should have been
解析：
试题分析: 考查情态动词。从对话可知此处问昨天的事，所以应该用情态动词+have done表示对过去的推测判断 ，排除A、C选项，must have done “肯定做过某事”，should have done “本应该做某事”，从语境判断B选项正确。句意：--汤姆，昨天下午为什么不接我电话呢？---对不起，我没听到。我肯定是睡着了。
