If players in a two player game play a Nash equilibrium
(a) there will always be an outcome that gives both players a higher utility than the Nash equilibrium;
(b) there will always be an outcome in which the sum of the two players' utilities is higher than in the Nash equilibrium;
(c) there can never be an outcome that gives both players a higher utility than the Nash equilibrium;
(d) there may, but need not be, an outcome that yields higher utility for both players than the Nash equilibrium.