Using appropriate demand, marginal revenue and cost curves, show graphs for the following situations. (Be sure to label the axes and curves and use numbers on your graphs to demonstrate that your graphs correctly show the condition specified in the question.
a. a natural monopoly subject to rate of return regulation
b. a monopolist with a short-run loss but continuing to operate
c. a perfectly competitive firm earning short-run economic profit
d. A monopolistically competitive firm in long-run equilibrium