​In a sequential game,given Mattie's best response function,what would Irene's best response be?

A) ​Not enter the market
B) Enter the market
C) Fight
D) ​Run away

Based on the given scenario, if Irene decides not to enter the market, she would earn zero profits. If Irene enters the market, Mattie has two possible options, either to accommodate Irene and share profits equally or fight a price war. If Mattie accommodates Irene, each would earn a profit of 5 million (half of the 10 million profits). If Mattie fights, both would earn a loss of 5 million each. However, if Irene enters the market, and Mattie's best response function predicts that the most rational option would be to accommodate Irene, then Irene's best response would be to enter the market as well. Therefore, given Mattie's best response function, the best choice for Irene would be to enter the market (option B).