What must be in place when a vehicle equipped with chocks is left unattended?

Answer: B — The chocks must be in place

When a vehicle equipped with chocks is left unattended, ensuring that the chocks are in place is crucial for safety and stability. Chocks are devices used to prevent a vehicle from rolling, especially when there is a slope or uneven ground. By placing the chocks correctly, you are effectively securing the vehicle in position and reducing the risk of accidental movement. While the engine being turned off and the vehicle having locked doors and closed windows are important safety practices, they do not specifically address the immediate concern of preventing the vehicle from rolling. Therefore, the presence of chocks directly targets the primary risk associated with leaving a vehicle unattended, making it the most critical requirement in this scenario.