During a pre-trip inspection, how should a driver check the bus brakes?

Pumping the brake pedal and listening for any unusual sounds is an effective method to assess the bus brakes during a pre-trip inspection. This procedure allows the driver to detect any potential issues, such as air leaks in air brake systems or malfunctions in the hydraulic system. When the brake pedal is pumped, the driver can feel for unusual resistance or softness in the pedal, as well as hear any irregular noises that could indicate worn-out parts or other problems that require attention.

The other options do not provide a comprehensive check of the brakes. While visually inspecting the brakes for damage is useful, it does not reveal functional issues that may be present. Deeply pressing the brake pedal once might not effectively assess the brake's performance under normal driving conditions. Checking only the brake fluid levels is important but does not cover the overall function and condition of the braking system. Therefore, the practical and proactive approach of pumping the brake pedal while listening for sounds is crucial for ensuring the brakes are in proper working order before driving.