Final answer:
The correct option is 4. When towing a loaded trailer that weighs more than one-half of the towing vehicle's weight or is 3,000 pounds or more, it must be equipped with brakes and breakaway protection.
Step-by-step explanation:
When towing a loaded trailer that weighs more than one-half of the towing vehicle's weight or is 3,000 pounds or more, the trailer must be equipped with brakes and breakaway protection.
Brakes are necessary to help the towing vehicle stop both itself and the additional weight of the trailer. Breakaway protection is essential in case the trailer becomes disconnected from the towing vehicle, ensuring that it will come to a safe stop. Hub caps are not directly related to the weight of the trailer and are not required for safety purposes.