Which statement best describes zero-sum games? a. they are games in which payoffs for both players are only positive. b. they are games in which payoffs are equal but opposite in magnitude for each player. c. they are games in which payoffs for one player are twice that of the other player. d. they are games in which payoffs for both players are only negative. e. they are games in which payoffs are initially negative for both players and progressively tend toward zero.