The mother found her baby ____ when she came home.

问题描述:

The mother found her baby ____ when she came home.
A.quite asleep B.sleeping fast
C.sound asleep D.fastly asleep

sound有熟睡的,酣睡的意思
在这里是形容他
已经睡着且睡得很熟
还有
found(find)表结果
其他三选皆表正在进行的动作
故不选