In Markets Characterized by Oligopoly

In markets characterized by oligopoly,

A) a small number of relatively large firms sell a differentiated product.
B) a small number of relatively large firms sell a standardized product.
C) mutual interdependence of firms means that actions of any one firm in the market will have an effect on the sales of all other firms in the market.
D) entry into the market is restricted so that profit may be positive in the long run.
E) all of the above.