2. The four largest firms in a market have the following market shares of total revenue: 20 percent, 15 percent, 10 percent, and 5 percent. The in this industry is .

A. four-firm concentration ratio; 50 percent B. four-firm concentration ratio; 750 percent C. Herfindahl-Hirschman Index; 50 D. Herfindahl-Hirschman Index; 2,500