Consider an Industry That Is Made Up of Nine Firms,each

Consider an industry that is made up of nine firms,each with a market share (per cent of sales) as follows:
A.Firm A: 30%
B.Firm B: 20%
C.Firms C,D and E: 10% each
D.Firms F,G,H and J: 5% each
What is the value of the four-firm concentration ratio and how is the industry categorised?

A) 50%;monopolistic competition
B) 70%;oligopoly
C) 75%;oligopoly
D) 80%;strongly oligopolistic