The four-firm concentration ratio Part 5 A. is accurate because it is based on estimates from the U.S. Census Bureau. B. is flawed in that it includes sales in the U.S. by foreign firms. C. is flawed in that it does not measure competition between industries. D. is accurate because it is based on national and global competition. E. is flawed in that it is calculated for local markets even though competition in some industries is national