gear pair with par-allel axes

例句：

1. 1. The car's engine isa complex gear system.
   汽车的发动机是一个复杂的齿轮系统。
2. 2. The train has several gears to adjust the speed.
   火车有多个齿轮来调整速度。
3. 3. The gears onthe clock are all in sync.
   钟表上的齿轮都同步了。