What should you do when parking your vehicle facing downhill with a curb?

Answer: B — Turn your wheels towards the curb.

When parking your vehicle facing downhill with a curb, it is important to turn your wheels towards the curb. This helps prevent your vehicle from accidentally rolling out into traffic. Turning your wheels away from the curb or parallel parking without turning your wheels would not provide the same level of safety and control. Choosing option D, that it doesn't matter which way you turn your wheels, is incorrect and could lead to a potential accident. It is important to always follow proper parking procedures to ensure the safety of yourself and others on the road.