gear pair with modified centre distance

例句：

1. 1.The car's engine is a complex gear system.
   这辆车的引擎是一个复杂的齿轮系统。
2. 2.The train has several gears to adjust its speed.
   火车有几个齿轮来调整速度。
3. 3.The machine uses gears to turn the screws.
   这台机器使用齿轮来转动螺丝。