Answer:D. It has some characteristics of monopolistic competition except there are few firms with significant market share.
Step-by-step explanation:
A monopolistic competition comprises of many producers whose products are differentiated, while in oligopoly market there is market dominance by a few producers.
The market has the features of both monopolistic competition and oligopoly combined, the competition of six hundred companies does make it an oligopoly, the product are not homogeneous so it cannot be a perfect market but rather it has the features of a monopolistic market because there are many producers selling differentiated products but the market dominance of few producers makes it an oligopoly.