1. Which of the following statements about negative extemalities is/are TRUE? 1. At the social-surplus maximizing level of output, external costs equal zero. II. At the unregulated competitive equilibrium, marginal social cost is greater than marginal social benefit. III. At any output level, social costs are greater than private (market) costs. a) I, II, and III. b) II only. c) III only. d) II and