In case of fog, can high-beam headlights be used?
A)Yes, outside built-up areas and if there is no risk of dazzling.Correct
B)No.
C)Yes, as long as it is between sunset and sunrise.
High-beam headlights could be used as long as we do not dazzle other users and we are not in a built-up area.
The problem is that with dense fog we may not be able to see other users on the road and may dazzle them or even dazzle ourselves, since fog consists of suspended droplets and the light beam can bounce off these droplets.
With heavy rain something similar happens; it usually reflects the light on the road markings, becoming bothersome.
The ideal is to switch on the low-beam or the corresponding fog light.