What is a gear train?

• A. When the driving mechanism of an engine consists only of gears
• B. A system using belts to transfer motion
• C. A hydraulic drive system
• D. A gear train is an arrangement of camshafts

Answer: (A)

A gear train is a set of gears arranged to transmit motion and torque from one shaft to another, changing speed and force through gear ratios. Saying the driving mechanism consists only of gears captures this idea: motion is passed entirely through gears, with their sizes determining how fast the output turns and how much torque it provides. The other options point to different systems—belts transfer motion with belts and pulleys, a hydraulic drive uses fluid pressure, and an arrangement of camshafts refers to valve timing components, not a general gear-based power transfer.