knock on

• 用手指关节敲击表面（如门）以引起注意或请求进入；也用于比喻接近某种情况或机会。

To strike a surface (such as a door) with the knuckles to gain attention or request entry; also used figuratively to mean approaching a situation or opportunity.

1. Strike a surfaceA1formal

   To hit a surface, typically a door, with the knuckles to gain attention or request entry.

   敲门

   • Please knock on the door before entering.
   • He knocked on the window to get her attention.
   • She knocked on the table to signal the start of the meeting.

2. Criticize or find faultB2informal

   To express negative opinions or criticism about someone or something.

   批评

   • Stop knocking on his efforts; he's trying his best.
   • Critics are always knocking on the new policy.
   • She tends to knock on everything she doesn't understand.