The Organization of Petroleum Exporting Countries (OPEC)controls About 75 Percent

The Organization of Petroleum Exporting Countries (OPEC) controls about 75 percent of the world's proven oil reserves.Economists refer to OPEC as a cartel because

A) OPEC is a monopoly, but it is located outside of the boundaries of any one country. This is the definition of a cartel.
B) this is the term used for an oligopoly that is controlled by national governments rather than private firms.
C) it is a group of firms that collude to restrict output to increase prices and profits.
D) this is the term economists use to describe an oligopoly that sells a standardized product, such as oil, rather than a differentiated product, such as automobiles.