What mandatory equipment must be on every heavy trailer?

The correct choice highlights essential safety equipment required on every heavy trailer. Safety chains are critical because they provide a secondary connection between the trailer and the towing vehicle, ensuring that the trailer does not completely detach in case of a hitch failure. Reflective triangles are vital for roadside safety; they alert other drivers to the presence of the trailer, especially in low visibility situations. A spare tire is also necessary as it allows for quick resolution of tire issues that may occur during travels, minimizing the risk of being stranded.

The focus on safety equipment illustrates the importance of preparedness when operating heavy trailers, which can often involve navigating busy highways or remote areas where assistance may not be readily available. This choice reflects regulations designed to ensure that drivers are equipped to handle emergencies that can arise while towing. Other options, while relevant in certain contexts, do not directly relate to mandatory equipment that guarantees safety and compliance during trailer operation.