Final answer:
When inspecting the air lines during a pre-trip inspection, look for visible cracks or damage to ensure the air brake system functions properly.
Step-by-step explanation:
During a pre-trip inspection of a vehicle with air brakes, you should: a) Look for visible cracks or damage. It's crucial to check the air lines thoroughly as they are essential for the proper functioning of the air brake system. Ignoring the air lines or checking only their exterior appearance is not sufficient because any internal damage or leaks could lead to brake failure. Measuring the length of the air lines is typically not relevant to a standard pre-trip inspection unless you have specific reasons to suspect they have been modified or replaced incorrectly. Air in the brake lines can lead to inefficient braking because a gas is compressible, and when force is applied, it would first compress and warm up. Therefore, the air must be bled out to ensure the brakes work effectively and safely.