What must you be prepared for in this situation?

You answered correctly because in this situation, all three things must be anticipated according to German traffic rules.

1. Oncoming traffic may suddenly appear from the opposite direction, hidden behind the truck parked ahead. This is especially likely because the truck is parked close to the edge of the road, blocking the view.
2. The truck driver might suddenly jump down onto the carriageway, for example, if they are about to move the truck or check something. As a precaution, you must be ready to react to them stepping onto the road.
3. Traffic signs may be concealed behind the truck. Since you cannot see the signs directly, you need to be cautious and assume that there might be important instructions or warnings hidden from your view.

Overall, this situation requires you to slow down, stay alert, and prepare for hidden hazards caused by the truck blocking your line of sight. This helps prevent accidents and ensures you drive safely.