What is a common method to check if the air brakes are functioning properly?

Answer: B — Perform a brake test before driving

Performing a brake test before driving is a crucial method to ensure that air brakes are functioning properly. This test typically involves checking for proper air pressure in the system and ensuring that the brakes engage and disengage correctly. During the brake test, the driver assesses the response of the brake system and looks for any unusual sounds or behaviors that may indicate a malfunction. This proactive approach helps identify issues before the vehicle is on the road, contributing to overall safety. Other methods listed, such as driving at high speed, checking brake lights, or solely observing warning lights, do not adequately assess the air brake system's condition. Driving at high speed can be dangerous and does not provide any meaningful insight into brake performance. Checking brake lights is essential for safety but does not reflect on the operational status of the braking mechanism itself. Observing warning lights may indicate a problem but does not involve a hands-on assessment of brake functionality. Therefore, the brake test stands out as the most reliable method for ensuring the air brakes are in proper working order.