(D) is correct because if only one ranger is assigned to area one - then we know it must either be J or K. M, O, P cannot be assigned to area 1 per rules 1 and 2. L must be assigned to an area with another ranger thus he cannot be the lone ranger in area one either, which leaves us with J or K. Per rule 4, if O is assigned to area 2, then J and K are assigned to the same area, but these are the only two rangers either of which could go to area 1, so if there were to be assigned to the same area, there would be no one left to go to area one. Thus, we can conclude that O cannot be assigned to area 2 and O cannot be assigned to area 1 per rule rule 2, hence O must be assigned to the only remaining area - 3.
(B) is incorrect because even though it could be true, it is not the case that K must always be assigned to area 2 if there is only one ranger in area 1. In fact, K could be that ranger in area 1 instead.
