knock kown

例句：

1. 1. The door was knocked open by the wind.
   门被风吹得敞开了。
2. 2. He knocked on the door gently.
   他轻轻地敲了敲门。
3. 3. The knock at the door signaled that someone was at the door.
   敲门声意味着有人在外面。