What is the primary control device of the air braking system?

Answer: C — Brake pedal

The primary control device of an air braking system is, indeed, the brake pedal. This device allows the driver to engage the brakes, thereby slowing down or stopping the vehicle effectively. In an air brake system, pressing the brake pedal sends a signal to the air compressor to build up air pressure in the braking system. This pressure is then used to apply the brakes at each wheel, making the vehicle stop. The brake pedal is crucial because it directly influences the amount of brake force applied. A proper understanding of how the brake pedal operates within the air brake system is essential for maintaining control of the vehicle and ensuring safety on the road. Other devices like the steering wheel and gear shifter serve distinct functions, such as controlling direction and selecting gears, while the clutch pedal is primarily used in vehicles with manual transmissions to disengage the engine from the wheels during gear changes. However, none of these play a role in the control of the braking system itself as the brake pedal does.