Under Regulation (EC) No 561/2006, what constitutes valid 'multi-manning' (Mehrfahrerbetrieb) during a passenger transport journey?

1. Two drivers employed by the same company, even if one travels by train to meet the bus at the destination
2. During each period of driving between two consecutive daily rest periods, or between a daily and weekly rest, at least two drivers are on board to do the driving; presence of the second driver is optional for the first hour only
3. A single driver accompanied by a tour guide who holds a Category B car driving licence
4. Two drivers where driver A drives for 9 hours and driver B sleeps in a trailer behind the bus