Which of the following best describes the competition in the U.S. online auction industry?

A) perfect competition

B) monopolistic competition

C) oligopoly

D) monopoly

Option C) oligopoly is correct

This option is correct because none of the firms can influence the market price in an oligopoly market. The perfectly competitive market consists of large firms that sell identical products, so it does not suit the online auction industry. The monopoly market consists only of one firm with no substitute available in the market, so this does not work in the online auction industry. The monopolistic competitive market is imperfect, so it does not work in the US online auction industry.