Many residents of a particular town enjoy taking their dogs with them when they go to their local park for recreation and picnics. Everybody enjoys the park more when each group cleans up after themselves and their pets, but nobody enjoys the act of cleaning up after themselves or their dogs. In this situation, we can expect the park to be due to a O clean: positive externality O clean: prisoner's dilemma 0 dirty : positive externality dirty:prisoner's dilemma