he_asleep when there_aloud knock at the door. A was just falling _英语解答

he_asleep when there_aloud knock at the door. A was just falling ;was D just fell;was
请问为什么不能选D .语法没错吧?谢谢了帮我解决下

人气：134 ℃　时间：2019-10-11 17:15:49

解答

when 前面表示的是一个睡着的状态属于时间段如选D fell asleep 则是一个瞬间动词,应该用现在进行时表示一个状态