问题补充：
单选题
I ________ asleep because it took me a long time to realize that the telephone was ringing.A.could fallB.need have fallenC.must have fallenD.may fall
网友答案：
热心网友 1楼
C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。
