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

According to William Shepherd's examination of competitive trends in the U.S.economy,if firms in the industry exhibit low concentration,low entry barriers,and little or no collusion,then the industry _____

A) is usually a pure monopoly.
B) is a dominant firm.
C) is a tight oligopoly.
D) demonstrates effective competition.
E) demonstrates monopolistic competition.