Three major means of collusion by oligopolists are

A) cartels, informal understandings, and price leadership.
B) market sharing, mutual interdependence, and product differentiation.
C) cartels, kinked-demand pricing, and product differentiation.
D) informal understandings, P = MC pricing, and mutual interdependence.

Collusion

Collusion is an agreement between two or more parties, often in secret, to limit open competition by deceiving, misleading, or defrauding others of their legal rights, or to obtain an objective forbidden by law typically involving fraud or gaining an unfair market advantage.

Cartels

An agreement between competing firms to control prices or exclude entry of a new competitor in a market, often resulting in higher prices and restricted competition.

Informal Understandings

Unofficial agreements or practices among firms or individuals that dictate behavior without being legally binding.