In case of very unfavourable weather conditions, such as very heavy rain, may you drive with the rear fog light switched on?
A)No, it can only be used in dense fog.
B)Yes, although its use is optional.
C)Yes.Correct
# Explanation
The rear fog light may be used in very adverse weather conditions, not only in case of dense fog. Very heavy rain significantly reduces visibility, so it is permitted to activate this light to improve the vehicle's visibility to other drivers travelling behind. The goal is to increase road safety when weather conditions are especially dangerous.