Final answer:
Vehicles must have at least two operable headlights and tailights to maintain visibility in poor lighting conditions. Headlights help with forward visibility while tailights make sure the vehicle is visible from behind.
Step-by-step explanation:
When visibility conditions warrant additional light, all vehicles or combinations of vehicles in use must be equipped with at least two operable headlights and tailights. Headlights are essential for maintaining visibility during poor lighting conditions, such as at night or in fog. The arrangement of the vehicle's mirrors and lights helps direct the beam of light for optimal illumination and visibility. Tailights, on the other hand, ensure that a vehicle is visible to others from the rear. It's crucial for safety that both headlights and tailights are functioning correctly to maintain good visibility of the road and surrounding environment.