What is the minimum amount of air you should have before beginning a trip?

Answer: C — At least 100 PSI.

Having a minimum of 100 PSI of air pressure before beginning a trip is essential to ensure the proper functioning of the air brake system. This pressure is necessary to guarantee that the brake system has enough stored energy to operate effectively throughout the journey. If the air pressure is below this threshold, the brakes may not engage properly, which can lead to increased stopping distances, brake fade, or even brake failure. Ensuring an adequate air supply contributes significantly to safety by allowing the driver to have reliable control over the vehicle under various driving conditions. Thus, starting your trip with at least 100 PSI ensures that the air braking system is fully prepared for safe operation.