A monopoly is a market characterized by:

a. a large number of small firms.

b. a product with many close substitutes.

c. a small number of large firms.

d. a single seller.

The answer is d.

A monopoly is a market that is characterized by (d) a single seller.

There are no close substitutes to the products offered by monopolies in the market, thus giving them a huge market share and market power. There are price setters and not takers since their decision to change price rarely affects demand. Firms in these markets are profit maximizers, thus engage in price discrimination. The market is often characterized by high entry barriers that may stem from high startup costs, control of natural resources, and economies of scale, among others. Monopolies might cause market inefficiencies.