Definition: a set of parts in a motor vehicle or bicycle that control how fast the wheels turn Level: B2
这辆山地自行车配备了21个齿轮。
This mountain bike is equipped with 21 ___gears.
这辆自行车配有24个活动齿轮。
The bike comes with 24 active ___gears.
在不同地形上骑行时，记得换挡。
Remember to change ___gears when cycling on different terrains.
