What should you check for in the air brake system during the pre-trip inspection?

Answer: B — Signs of leaks and correct air pressure

During the pre-trip inspection of an air brake system, it is essential to check for signs of leaks and ensure that the air pressure is correct. This is crucial because air brakes rely on compressed air to function properly. Leaks can lead to a loss of air pressure, which can affect braking performance and compromise safety on the road. Ensuring that the air pressure is within the recommended range is vital for the effective operation of the brakes. Proper air pressure ensures that the brakes engage correctly and can stop the vehicle as needed. The other options, while they contain important elements for vehicle safety, do not specifically address the unique requirements of an air brake system. For instance, brake fluid levels are relevant for hydraulic braking systems, but not for air brakes. Tire pressure is important for overall vehicle safety but is not specific to the air braking system itself. Checking brake shoe thickness and electric connections pertains more to conventional or electric braking systems than to air brakes. Similarly, friction material and light functionality are critical for vehicle operation but also do not specifically apply to the air brake system's pre-trip inspection.