What is the minimum number of head lamps that must be illuminated on the front of a vehicle at night?

The requirement for the minimum number of headlamps that must be illuminated on the front of a vehicle at night is centered around ensuring adequate visibility for safe operation. A vehicle is required to have at least one headlamp on each side (which typically means two in total). This is crucial for providing a balanced distribution of light, improving visibility for both the driver and oncoming traffic, and allowing for better identification of the vehicle's size and position on the road.

Having one headlamp on each side ensures that the vehicle is clearly visible from different angles, which enhances safety. The other options suggest either fewer or more than the required number, which do not align with the standard regulations that prioritize both visibility and roadway safety in nighttime driving conditions. Hence, option A is the most appropriate choice when considering the stipulated safety regulations for headlamp usage on vehicles.