Point out one product that you believe is produced by a "pure" monopoly firm (or a firm with a high degree of monopoly power). Is it a local, regional or national monopoly? What are some of the Barriers to Entry into this industry?
For the product listed, list substitute(s) for this "monopolies."
Demonstrate how the relative "closeness" of the substitutes listed determines, to a large degree, effective limits to the monopoly power of these firms.