Which vehicles must always be marked by their own lights or parking warning plates when parked on the roadway at dusk or in darkness in built-up areas?

The selected combination is correct because, according to German traffic regulations, both trucks and motor caravans with a permissible total mass exceeding 3.5 t and trailers must always use their own lights or parking warning plates when parked on the roadway at dusk or in darkness in built-up areas. This rule is important for ensuring visibility and safety on the roads, particularly in areas where pedestrian and vehicle traffic is high. By marking these larger vehicles, other road users can better see them, reducing the risk of accidents. Cars do not require this marking under the same circumstances, which is why they are not included in the correct combination. Understanding these requirements helps in promoting safe parking practices and adherence to traffic laws.