Which of the following is a requirement for the air pressure gauge check?

The requirement that the air pressure gauge should be within normal operating range is crucial for ensuring that the vehicle's braking system is functioning properly. The air pressure gauge provides important information about the air pressure in the braking system, which is essential for the safety and effectiveness of the vehicle’s braking capabilities. If the gauge indicates that the air pressure is too low, it could mean that the brakes will not engage properly, posing a significant risk of failure during operation.

Maintaining air pressure within the normal operating range helps to ensure optimal performance and enhances the overall safety of the vehicle. It's a fundamental aspect of regular pre-trip inspections, as improper air pressure can lead to critical failures on the road.