knock|knocks|knocked|knocking

有人在敲门。

Someone is ___knocking on the door.

进入前请先敲门。

Please ___knock before entering.

今天一大早，有人敲了我的门。

Early this morning, someone ___knocked on my door.

他在进入前敲了三下门。

He ___knocks on the door three times before entering.