Why do economists believe an oligopolist'sdemand curve may be kinked?

A The government may collude with the firm to cause that type of shape.

B The oligopoly firms "cheat"and mark up prices to create that shape.

C If oligopolistsdon't collude, they may still find that competitors ignore price increases, but match price decreases.

D Intense competition may drive them to the position where the demand curve has a kink.