What is the primary function of air brakes in commercial vehicles?

Answer: B — To slow or stop the vehicle using compressed air

The primary function of air brakes in commercial vehicles is to slow or stop the vehicle using compressed air. Air brakes operate by utilizing air pressure to apply the brake shoes against the wheels, creating friction that slows down or halts the movement of the vehicle. This system is particularly advantageous in heavy-duty trucks and buses because it can handle the significant braking requirements necessary for larger vehicles. While the other options may describe functions or benefits associated with vehicles in general, they do not accurately reflect the specific role of air brakes. Accelerating a vehicle with compressed air is not a function performed by air brakes. Instead, air brakes are designed for deceleration and safe stopping. Similarly, while improving fuel efficiency and enhancing engine performance are important aspects of vehicle design, they are not the primary function of braking systems. Thus, focusing on the role of air brakes in controlling a vehicle's speed is essential for understanding their operation in commercial vehicles.