The Market Concentration Ratio

The market concentration ratio:

A) shows the percentage of total sales or production accounted for by the four largest firms in an industry.
B) is a widely used, reliable measure of an industry's market structure.
C) was developed by a Swedish and a German statistician in the late 1890s.
D) shows the percentage of total sales or production accounted for by the 10 largest firms in the United States.
E) is so flawed a measure of an industry's market structure that it is almost never used.