knock

She knocked on my door three times before I realized someone was there.

(Chinese) 她在门上敲了三次，我才意识到有人在那里。

Please knock before entering the meeting room to avoid interruptions.

(Chinese) 进入会议室前请先敲门，以免打扰。

I heard a loud knock at the window in the middle of the night.

(Chinese) 半夜里我听到窗户上传来一声清脆的敲击声。

The engine started making a strange metallic knock whenever it accelerated.

(Chinese) 每当加速时，发动机就开始发出一种奇怪的金属敲击声。