2. In the small town of Geneva, there are 5 firms that make watches. The firms’ respective output levels are 30 watches per year, 20 watches per year, 20 watches per year, 20 watches per year, and 10 watches per year. The four-firm concentration ratio for the town’s watch-making industry is [LO12.1]

a. 5

b. 70

c. 90

d. 100