4. Two firms simultaneously decide what price to advertise in the weekly newspaper. Both firms make zero profit if they both charge a low price. Both firms earn $3 if they both charge a high price. If the firms charge different prices, the one charging the higher price loses $5 and the one charging the lower price makes $5. Consider a trigger strategy: high price provided no one has ever charged a low price in the past; and if any firm charges a low price, "punish" the firm by choosing the one-shot Nash equilibrium strategy forever after. Which statement is wrong? A. A trigger strategy stipulates that each player uses the history of what its rival did to decide whether it should cooperate or not. B. Whenever one player cheats in the previous period, its rival should choose not to cooperate. C. Both players charging high price is a unique Nash equilibrium for a one-shot version of the game. D. Suppose the game is infinitely repeated and the discount rate is 0.9. The cooperative (collusive) outcome can be sustained in the infinitely repeated game