What Is True Regarding an Oligopoly

What is true regarding an oligopoly?

A) Prices charged by different firms stay fairly close because a price cut or increase by one company will trigger a similar response from another company.
B) The prices charged by different firms vary widely, since each firm can charge whatever it wants.
C) In oligopolies, it is inexpensive for new firms to enter the marketplace.
D) Prices never change because the government has set the products' price.
E) Since there are very few businesses selling the product, there is no need to ever change the price.