问题补充:
I asleep because it took me a long time to realize that the telephone was ringing.
A. could fall
B. need have fallen
C. must have fallen
D. may fall
答案:
A. could fall
B. need have fallen
(答案→)C. must have fallen
D. may fall
解析:考查情态动词表示推测的用法。must have done 表示对过去事情肯定的推测,句意:我当时一定是睡着了,因为花了我好长一段时间才意识到电话正在响。故选C。