How can the air brake system be properly vented?

Answer: C — By opening the bleed valve

The air brake system is properly vented by opening the bleed valve. This action allows air to escape from the system, which is crucial for releasing pressure accumulated in the brake lines and ensuring that the system can reset itself before being recharged. When the bleed valve is opened, it facilitates the expulsion of any residual air, which helps to clear and maintain the integrity of the air brake system. This process is fundamental to ensuring that the brakes work effectively, as trapped air can cause brake failure or poor performance. Proper venting also helps to avoid issues such as brake drag, where the brakes do not release fully, leading to increased wear and potential overheating of the components. Opening the bleed valve is therefore a standard procedure in the maintenance and operation of air brake systems to ensure they function correctly and safely.