Answer: D) Monopolistic competition
Explanation: Monopolist competition is the competition in the marketing field by selling the products which are different from each other on basis of certain parameters such as brand.
According to the situation mentioned in the question ,presence of 12 airlines for opting are huge amount where airplane is viewed from product point of view and thus, it will create a imperfect competition.
Other options are incorrect because perfect competition is raised by the perfect market of products, monopoly is the situation with no competition and oligopoly is the competition with limited number of seller and their products.Thus, the correct option is option (D).