When driving in fog, you should use:

Using low beam headlights when driving in fog is important for safety and visibility. High beam headlights can actually create glare and make it more difficult to see, as the light reflects off the fog, rain, or other moisture in the air. This can obscure your view and reduce your visibility significantly.

Low beam headlights provide a more focused and direct light that is less likely to reflect back into the driver's eyes. This helps maintain visibility on the road and allows you to see other vehicles, pedestrians, or obstacles more clearly. Additionally, using low beams helps other drivers see you without the risk of blinding them, which is especially crucial in conditions where visibility is reduced.

Parking lights alone are not adequate for driving, as they do not provide sufficient illumination for the road. Not using any lights at all during fog can be extremely dangerous, as it may not only reduce your visibility but also make it difficult for other drivers to see you. Utilizing low beam headlights in foggy conditions is clearly the best and safest choice.