A. The number of actual market competitors is relevant to the level of competitiveness B. Potential competition is the same as actual competition when sunk costs are zero C. Sunk costs have nothing to do with market contestability since sunk costs are in the past D. The more sunk costs, the more hit and run entry tactics used by competitors E. In a perfect contestable market, a single seller behaves like a monopolist (restricting output and raising price)