please do both parts in 15 minutes please urgently and give only final answer no need to explain... I'll give you up thumb definitely

11. Which of the following is true? O In Bertrand oligopoly each firm believes that their rivals will hold their output constant if it changes its output. In Cournot oligopoly firms produce an identical product at a constant marginal cost and engage in price competition. O in oligopoly a change in marginal cost never has an effect on output or price. O None of the statements associated with this question are true. 18. Which of the following is not a quantity-setting oligopoly model? Cournot. Bertrand. Stackelberg