Which external lighting devices must without fail be turned on when a vehicle combination is travelling during the hours of darkness, regardless of the degree of road illumination?

1. 1Low-beam or high-beam headlights on the tractor and marker lights on the trailer.
2. 2Marker lights on the tractor unit and the trailer.
3. 3Low-beam headlights on the tractor and a rear fog light on the trailer.
4. 4Fog lights on the towing vehicle and marker lights on the trailer.