The law requires a trailer with an all up weight of more than 4,000 kg to have:

1. Correct answer: An "additional license plate" to be installed on the trailer's rear.
2. License plates which are twice the size of regular plates.
3. A trailer in such a weight doesn't require license plates at all.
4. An "additional license plate" to be installed on the trailer's front.

WhyA trailer over 4,000 kg must have an additional license plate at the rear, where the vehicles following it can see it.