Suppose the Market for Gasoline Retailing (Gas Stations)in an Island

Suppose the market for gasoline retailing (gas stations) in an island economy has 12 firms.The two largest firms each account for 30% of sales,the third accounts for 15%,the fourth for 7%,the fifth for 4% and the remaining firms for 2% each.Which of the following statements best describes the structure of this local industry?

A) This industry is an oligopoly.
B) This industry is perfectly competitive.
C) This industry is a monopoly.
D) This industry is monopolistically competitive.
E) Either A or D could be correct.