求翻译：机器由许多机械零件组成。最常用；来传动的机械零件是齿轮。齿轮实际上是个带有很多个齿的轮子。齿轮必须成对工作。齿数不同的一对齿轮能够提高或降低转速。是什么意思？

The machine is composed of many mechanical parts. The most commonly used; to drive the mechanical parts of the gear. The gear is actually with a lot of gear wheels. The gear must work in pairs. Number of teeth a different pair of gears to increase or decrease the speed.

Machine generated by a number of mechanical parts. The most commonly used; to drive the mechanical parts is a gear. In fact, a gear with a lot of tooth wheels. Gear must work in pairs. Depending on the number of teeth on a gear to be able to increase or decrease speed.

Machine is made