grating of gears

例句：

1. 1. The car's engine is a complex system of gears and belts.
   汽车的引擎是一个复杂的齿轮和皮带系统。
2. 2. The engineer carefully adjusted the gears to match the machine's specifications.
   工程师仔细调整了齿轮，以符合机器的规格要求。
3. 3. The old clock had worn out its gears and needed to be replaced.
   旧时钟磨损了它的齿轮，需要更换。