Five rooms of a house are to be painted in such a way that rooms with an interconnecting door have different colors. If there are n colors available, how many different color schemes are possible when the rooms in the house are arranged in the following way?

(a) Connected rooms form a linear order with one door interconnecting two adjacent rooms.

(b) Connected rooms form a linear order with one door interconnecting two adjacent rooms. The first and last rooms must be colored differently.

(c) Connected rooms form a circular order with one door interconnecting two adjacent rooms.