Which device is used by drivers to change gears in a manual transmission vehicle?

In a manual transmission vehicle, the clutch is the essential device that allows drivers to change gears. When a driver wants to shift from one gear to another, they must depress the clutch pedal. This action temporarily disengages the engine from the wheels, enabling a smooth transition between gears without causing damage to the transmission. The clutch is critical for controlling the power transfer from the engine to the wheels during gear changes, making it possible to increase or decrease speed as required.

The brake pedal and accelerator pedal serve different functions, primarily related to stopping the vehicle or controlling speed, respectively, and are not involved in the gear-changing process. The shift indicator is a display that shows the current gear engaged but does not aid in the physical act of shifting gears. Therefore, the clutch is the correct answer, as it directly facilitates the changing of gears in manual transmission vehicles.