If you have to park in fog, what should you use?

Answer: C — sidelights (parking lights)

When parking in fog, it is important to use sidelights, also known as parking lights. This is because parking lights are less bright than low beam headlights, reducing glare for other drivers in the fog. High beam headlights and hazard lights are not suitable for parking in fog as they may be too bright and can disrupt the vision of other drivers on the road. Additionally, using no lights at all can be dangerous as it makes it difficult for other drivers to see your parked vehicle in the fog. Therefore, using sidelights is the safest and most appropriate option when parking in fog.