Before shifting into a lower gear, what must be done to the engine speed?

The correct answer indicates that before shifting into a lower gear, the engine speed must be increased to match the speed of the gear. This process, often referred to as "rev matching," helps ensure a smooth transition between gears. When shifting to a lower gear, if the engine speed is not adequately adjusted, it can lead to grinding of gears, increased wear on the transmission, and potentially can cause the vehicle to jerk or lurch due to mismatched speeds.

By increasing the engine speed before the downshift, the engine can more easily accommodate the change in the gearing ratio, allowing the drive wheels to remain engaged smoothly without losing traction or risking damage to the driveline components. This practice is especially important in performance driving and certain driving conditions where precise handling is necessary.

Other potential choices would not facilitate a smooth shift. For instance, simply maintaining the current speed could create a jarring transition, while stopping the vehicle completely would render the shift unnecessary. Decreasing the engine speed to match the lower gear would exacerbate issues with gear engagement, potentially leading to incomplete shifts and mechanical stress.