When must headlights be on?

Answer: C — During any weather conditions

Headlights must be on during any weather conditions, not just after dark or during the night. They are an essential safety feature that provides visibility for both the driver and other vehicles on the road, especially during inclement weather such as rain or fog. While headlights are necessary during these times, they should also be used during clear daytime hours to ensure the vehicle is visible to others on the road. Government regulations also require headlights to be on when visibility is reduced to 500 feet or less. Therefore, option A and B are incorrect as they do not encompass all necessary conditions for headlights to be used. Option D may seem like a logical choice, however, it is important to note that the time of day varies greatly in different locations and does not take into account weather conditions. Thus, option C is the most accurate and inclusive choice.