What is an acceptable condition for the air lines?

The correct answer emphasizes that air lines must be in a pristine condition without signs of wear or damage. This means there should not be any abrasions, cuts, fraying, or exposed wires, which could compromise their structural integrity and lead to potential failures or leaks during operation.

Maintaining the air lines in an acceptable condition is crucial for the braking system's functionality and safety of the vehicle. Any sign of deterioration, such as cuts or fraying, could increase the risk of experiencing a loss of air pressure, which may affect braking performance and overall vehicle operation. Hence, the criteria in the correct answer focuses on ensuring that the air lines are completely intact and operational without any issues that could jeopardize safety.