It Is Harder to Explain the Behavior of Firms in an Oligopoly

It is harder to explain the behavior of firms in an oligopoly than in other market structures because _____

A) the firms act independently of each other in an oligopoly.
B) firms base their decisions on what their rivals do.
C) only differentiated products are produced by firms in an oligopoly.
D) only homogeneous products are produced by firms in an oligopoly.
E) the demand curve faced by a firm in an oligopoly can slope upward.