The United States Postal Service has a monopoly on non-urgent First Class Mail and the exclusive right to put mail in private mailboxes. Pfizer Inc. makes LIPITOR, a prescription drug that lowers cholesterol. Cox Communications is the sole provider of cable television service in some parts of San Diego.

a. What are the substitutes, if any, for the goods and services described above?

b. What are the barriers to entry, if any, that protect these three firms from competition?

c. Which of these three firms, if any, is a legal monopoly? Explain your answer.

d. Which of these three firms are most likely to be able to profit from price discrimination and which are most likely to be able to sell their good or service for a single price?