LocCloud-
knock at the door.
To see the manager, knock at the door marked"private".
要见经理，请敲标有“私人的”字样的房间。
When I heard the knock at the door, was the frightened out of my senses.
一听见有敲门声我就吓得六神无主。
ardim-
knock at the door
He is knocking at the door.
北境漫步-
knock at [on] a door
我不懂运营-
knock at [on] a door
苏萦-
to knock at the door
小教板-
knock on a door
knock at a door
wio-
Knock on: 敲（门、窗等）
例句与用法:
1. He accidentally knocked on (the pass from Jones). 他非故意犯规, 用手向前击了（从琼斯传来的）球.
2. Jim sat up when he heard the knock on his bedroom door. 吉姆听到敲寝室门的声音时便坐了起来。
3. Please do not enter before knocking on the door. 进来前请先敲门。
Knock at: vt. 敲 例句与用法:
1. There was a furious knock at the door. 有人在猛烈地敲门。
2. Did I hear a knock at the door? 是有人敲门吗?
3. Did you hear the knocks at the door? 你听到敲门声了吗
这两次词的区别不是很大，有时可以通用，但是一般表示敲在人身上的某个部位习惯用knock on 而不是knock at .如: Knock on her head 等。