Answer:
The correct answers are letters "A", "B", and "D": Difficult entry, Market control by a few large firms; Mutual interdependence.
Explanation:
An oligopoly is when a small group of two or more large firms controls the market. Oligopolistic firms may contribute to market collusion, and build obstacles to new trade entry. If the companies do not, they are likely to be forced to lower their prices and open the market to smaller companies.