What is one reason a license plate must be kept clean?

Answer: D — To ensure visibility for law enforcement

A license plate must be kept clean primarily to ensure visibility for law enforcement. When drivers operate a vehicle, law enforcement officers rely on being able to read the license plate numbers clearly and quickly, especially in situations where identification of a vehicle is necessary for traffic stops, investigations, or monitoring compliance with the law. If a license plate is dirty or obscured, it can hinder law enforcement's ability to identify vehicles involved in criminal activities or traffic violations. This visibility is essential not only for enforcement purposes but also for the overall safety and order on the roads. While there are other considerations, such as ensuring that tolls are processed properly or avoiding fines, the fundamental need for law enforcement to clearly see and read the plate takes precedence.