Question

I ________ asleep because it took me a long time to realize that the telephone was ringing.

1. A.
   could fall
2. B.
   need have fallen
3. C.
   must have fallen
4. D.
   may fall

Answer 1

C
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。