The following excerpt is from "Throwing the Book at Apple" (Wall Street Journal, Review and Outlook, June 12, 2013): At the time, prior to the existence of the tablet device market that Jobs created with the iPad, Apple did not sell eminus−books. Amazon sold nine of every 10. Justice claims Jobs then forced Amazon and every other eminus−book distributor to adopt a new eminus−book pricing model that harmed consumers. Yet the average retail price for "trade" eminus−books has since dropped to $7.34 from $7.97, and Amazon's Kindle is still the industry leader with Apple trailing in third. Over the same period readers bought 447% more eminus−books, and they can choose from dozens of tablets for titles and other media content.
What market structure best describes the e - book market?
A. A monopoly
B. A perfectly competitive market
C. A competitive market with a few dominant firms producing identical goods
D. A competitive market with a few dominant firms producing substitutes