What must you do when leaving your vehicle unattended?

Answer: D — All of the above.

When leaving your vehicle unattended, it is crucial to take several precautions to ensure the safety and security of the vehicle. Stopping the engine prevents any accidental movement of the vehicle while it is unattended, reducing the risk of damage or accidents. Locking the ignition and removing the key is essential to prevent unauthorized use of the vehicle, which helps deter theft. Additionally, setting the parking brake is an important safety measure, especially on inclines, as it ensures that the vehicle does not roll away. In combination, these actions create a comprehensive approach to vehicle security and safety when you are not in attendance, making it essential to perform all of them each time you leave your vehicle.