Answer:
The correct answer is letter "C": duopoly.
Step-by-step explanation:
Duopolies are the extension of oligopolies in which two companies dominate a market. In case the two companies collude to set a price for the products or services they provide, a duopoly becomes an oligopoly. However, that practice is forbidden by U.S. antitrust laws. Airbus and Boeing represent a duopoly in the aircraft market.