Final answer:
Option B). The brake pedal in an air brake system controls the air pressure applied to put on the brakes, using principles similar to those in hydraulic brake systems but with compressed air.
Step-by-step explanation:
In an air brake system, the brake pedal regulates the air pressure used to apply the brakes. Pascal's principle is applied when a driver presses the brake pedal, increasing the force applied through a series of levers and ultimately through the hydraulic system. After that, the same amount of force is applied to the wheel cylinders, which pressurize the brake shoes or pads to stop the car. While the idea behind hydraulic and air brake systems is similar, compressed air is used in air brake systems rather than brake fluid to generate the required pressure. For heavy-duty trucks and buses, where a greater braking force is necessary to safely control the large mass of these vehicles, this kind of system is essential. It is important to note that the brake system must be free of air in the lines to function efficiently, as air is compressible and would otherwise compromise the system's performance.