上齿轮

例句：

1. 1. The car's engine is running smoothly because the gears are properly adjusted.
   汽车的引擎运行顺畅，因为齿轮调整得当。
2. 2. The old clock had worn out its gears and needed to be replaced.
   旧时钟的齿轮磨损了，需要更换。
3. 3. The train's wheels were in perfect sync with the gears of the train's motor.
   火车的车轮与火车电机的齿轮完美同步。