What is required on the rear of every pole trailer?

The requirement for pole trailers is that they must have specific lighting and reflectorization to ensure visibility and safety, especially during nighttime or low-light conditions. The correct answer emphasizes that two red stop-lamps must be located on each side of the trailer. This requirement is crucial for alerting drivers behind the trailer when the vehicle is stopping or slowing down.

Having two stop-lamps on each side enhances visibility, ensuring that other road users can clearly see when the pole trailer is preparing to stop. This is important given the often long and narrow profile of pole trailers, which can make them less noticeable compared to standard vehicles.

The other options might include important features, but they do not satisfy the specific requirement for pole trailers regarding stop-lamps. Only one stop-lamp or colored reflectors would not provide adequate warning for drivers behind the trailer, which is why the two red stop-lamps on each side are mandated for safety.