If the Four-Firm Concentration Ratio for Industry X Is 60

If the four-firm concentration ratio for industry X is 60,

A) the four largest firms account for 60 percent of total sales.
B) each of the four largest firms accounts for 15 percent of total sales.
C) the four largest firms account for 60 percent of total advertising expenditures.
D) the industry is monopolistically competitive, but on the threshold of being an oligopoly.