What could happen if air tanks are left un-drained?

Answer: B — Moisture buildup could cause brake failure

Leaving air tanks un-drained can lead to moisture buildup, which poses a significant risk to the braking system. When moisture accumulates in the air tanks, it can freeze in cold weather or react with the components of the brake system. This could result in corrosion of the brake parts, leading to reduced effectiveness of the brakes or even complete brake failure. Thus, proper maintenance, including regularly draining the air tanks, is crucial to ensure that the braking system operates safely and effectively. This option highlights the importance of maintaining both the mechanical parts and the air supply system to prevent potential hazards on the road.