Choose one

subgame perfect equilibrium is: When all players always play their dominant strategies. When player 1 adopts her the strategy that provides the highest payoff, regardless of the strategy of its rival. Each player adopts the best response to the strategies of their rivals, however these strategies do not need to be credible. Each player adopts a strategy that provides the highest payoff given the strategies of their rivals, where they would implement the strategy at all parts of the game, even if that part of the game is not actually reached in equilibrium (that is in sections of the game off the equilibrium path on the game tree)