knocking of the valve

例句：

1. 1. The sound of the kettle's knob being knocked against the saucepan was a familiar one.
   水壶旋钮被敲打在锅上的声音是熟悉的。
2. 2. As he entered the room, he noticed that someone had knocked at the door.
   他走进房间时，注意到有人敲了门。
3. 3. The knocking at the door grew louder as more people arrived.
   随着越来越多的人到来，敲门声越来越响。