Which vehicle may legally use 100 km/h on a Belgian motorway?

1. An autobus with a few standing passengers if the limiter shows 100
2. An autocar with three unbelted folding seats as long as the limiter is set to 100
3. An autocar on which every seat has a belt and the limiter is set to a maximum of 100 km/h
4. Any DE combination, because the trailer stabilises the coach