The stage at which people develop the ability to think abstractly is the:

In which of the following games is it clearly the case that the cooperative outcome of the game is good for the two players and bad for society? a. two oil companies own adjacent oil fields over a common pool of oil, and each company decides whether to drill one well or two wells. b. two airlines dominate air travel between city a and city b, and each airline decides whether to charge a "high" airfare or a "low" airfare on flights between those two cities. c. two superpowers decide whether to build new weapons or to disarm. d. in all of the above cases, the cooperative outcome of the game is good for the two players and bad for society