Final answer:
Commercial trucks and trailers are vehicles that must have mud flaps for safety reasons.
Step-by-step explanation:
In many countries, vehicles that are required to have mud flaps are commercial trucks and trailers. This is because mud flaps help to prevent mud, rocks, and other debris from being kicked up by the tires and hitting other vehicles or pedestrians. By having mud flaps installed, these vehicles can help to keep the roads safer and reduce the risk of accidents or damage to other vehicles.
It is important to note that the specific regulations regarding mud flaps may vary from country to country and even within different regions of the same country. Therefore, it is advisable to consult local laws and regulations to determine the requirements for mud flaps.