At which places where there are no traffic signs regulating priority does the rule "right before left" apply?

The “right before left” rule in Germany applies at intersections or junctions without priority signs, traffic lights, or other rules indicating who has the right of way. This rule states that you must yield to vehicles coming from your right. However, it only applies at regular crossroads and junctions—so answer 1 ("At crossroads and junctions") is correct. It does not apply at places like junctions with sunken kerbstones or junctions where farm or forest tracks meet main roads, as those are exceptions: here, vehicles coming from those side roads must always yield. Remember: if there are no signs and no kerbstone or farm/forest track situation, yield to the right. This principle will help you in similar situations on the road.