According to William Shepherd's Examination of Competitive Trends in the U.S.economy,a

According to William Shepherd's examination of competitive trends in the U.S.economy,a dominant firm _____

A) is usually a pure monopoly.
B) is a firm with over half the market share and no close rival.
C) is one of four firms that together supply more than 60 percent of the market.
D) is a firm that sells a product with many close substitutes.
E) is one of four firms that work together to block entry into the market.