When parking your vehicle downhill without a curb, you should turn your wheels:

Answer: A — Towards the roadside.

When parking on a downhill slope without a curb, it is important to turn your wheels towards the roadside. This is because, without a curb, there is a possibility that your car may roll into traffic if the brakes fail. By turning your wheels towards the roadside, the curb can act as a barrier and prevent your car from rolling into oncoming traffic. Options B and C are incorrect as they do not offer any protection against a potential roll towards traffic. Option D is also incorrect because the direction of the wheels does matter in this situation to prevent any potential accidents.