Correct Answer: (c) Oligopoly
Solution:In an oligopoly market structure, a small number of large firms dominate the market. In the case of the mobile phone operators market in India, there are a few major players such as Jio, Airtel, Vodafone, and Idea, who control a significant portion of the market share. These firms have a significant influence over the pricing and output decisions, and they often compete on factors such as network coverage, pricing plans, and customer service.