Why can it be dangerous to overtake on an unobscured, straight road?

Your selected combination is correct because each of the points you identified highlights a crucial risk involved in overtaking on a straight road.

1. Underestimating the distance of an oncoming vehicle can lead to dangerous situations where a driver believes they have ample time to overtake, only to find out the vehicle is closer than they thought.
2. Overestimating the speed of an oncoming vehicle can result in making a hasty decision to overtake, leading to potential collisions.
3. Misjudging the overtaking distance can cause a driver to miscalculate how much space they need to safely pass, increasing the risk of accidents.

German road rules emphasize the importance of proper judgment and awareness of surrounding traffic to ensure safety during maneuvers like overtaking. Understanding all these aspects helps drivers make informed and safe decisions on the road.