I have no idea what while I was asleep.
A. has happened
B. could happen
C. had happened
D. happened
网友回答
A. has happened
B. could happen
C. had happened
(答案→)D. happened
解析：
试题分析:考查动词时态。从语境可知发生的事情应该是在说话人睡觉期间，应该用一般过去时，而C选项过去完成时需有过去的时间或过去的动作做对照才可以使用， B选项表示将来可能发生，不合句意，故D选项正确。句意：我不知道当我睡着的时候发生了什么事情。