Hardly asleep when someone knocked at the door.A she had fallen B she fell C had she falle

问题补充：

Hardly asleep when someone knocked at the door.

A,she had fallen B,she fell C,had she fallen D,did she fall

答案：

解析：when引导的时间状语从句，从句时一般过去时，主句要用过去完成时。又因为表示否定意义的词Hardly位于句首，故主句用部分倒装。