Suppose that Thierry and Abdul are duopolists. Thierry is producing 700 units of output, and Abdul is producing 500 units of output. When Abdul produces 500 units, Thierry maximizes profit by producing 700 units. When Thierry produces 700 units of output, Abdul maximizes profit by producing 500 units. Thierry and Abdul are

a. pricing at the minimum of marginal cost.
b. in a competitive market.
c. at a Nash equilibrium.
d. engaging in mark-up pricing.

c