Which of the following statements about oligopoly markets is correct?

Group of answer choices

A.) In a Cournot duopoly, if my rival's marginal cost increases, then my best response function will shift right.

B.) If firms' products are homogeneous but marginal costs differ, then total producer surplus among Bertrand duopolists will be positive.

C.) Bertrand reaction functions are only upward sloping if products are differentiated; otherwise, they are flat and equal to marginal cost.

D.) If firms have homogeneous products and identical costs, Cournot and Bertrand prices will be equal.