The four firm concentration ratio is:

A. The average price elasticity of demand for the largest four firms in an industry.

B. The ratio of the largest four firms' profits in an industry to the total profits of the remaining firms in the industry.

C. The largest four firms' share of industry revenues, who have market power when the four-firm concentration ratio is 40% or higher.

D. A measure of collusion among the biggest four firms in an industry.