Final answer:
When towing a trailer, you need to ensure it has proper wheels, tires, and lighting equipment.
Step-by-step explanation:
When towing a trailer, you must ensure that it is equipped with wheels properly mounted and lubricated, and covered with fenders or mud guards. Additionally, you need to have good tires properly inflated. Lastly, the trailer should have tail, stop, turn signal, license plate, and if required, side marker lamps and reflectors.
Therefore, the correct answer is option 4: All of the above.