Every oligopolist

A) is part of a cartel.
B) colludes openly.
C) can ignore the actions of her competitors.
D) takes into account the actions of her competitors.

Oligopolists take into account the actions of their competitors in order to make strategic decisions about prices, output, and marketing. While some oligopolists may collude and form cartels to act as a single dominant firm in the market, this is not always the case. Therefore, A and B are incorrect. Similarly, oligopolists cannot ignore the actions of their competitors, as they are interdependent in the market. Therefore, C is also incorrect.