What must not be placed on the windshield of a vehicle?

The correct response is focused on the critical importance of ensuring clear visibility for the driver. Any material that obstructs visibility can significantly impair a driver's ability to see the road, other vehicles, pedestrians, traffic signs, and signals. This lack of visibility can lead to accidents and unsafe driving conditions. Therefore, laws and regulations emphasize that nothing should be positioned on the windshield or any area that could block the driver's view.

In contrast, while sun visors, air fresheners, and insurance stickers are common items found in vehicles, they are generally either designed not to obstruct the driver's view or are positioned in ways that comply with visibility regulations. For example, sun visors are specifically designed to improve visibility by blocking sunlight and are positioned to avoid obstructing the driver's field of view. Air fresheners and insurance stickers, if placed correctly, do not hinder sightlines necessary for safe driving.

Thus, placing any item that obstructs visibility poses a direct risk to safety and violates traffic safety regulations.