临界的

So the young security man ordered me to pass through the door alarm again. I did.

保安让我再从带警报的门走一次，我去了。

This article has introduced noise reduction principles and methods, formation mechanism of vehicle exhaust noise, sorts of vehicle exhaust mufflers.

本文系统介绍了噪声控制的方法，汽车排气噪声的产生机理以及车用排气消声器的种类。