An economy produces only two goods, pizzas and cakes. If the opportunity cost of pizzas in terms of cakes is equal to 1/2, then
a. in order to produce one more pizza, the economy needs to give up on half a cake
b. in order to produce one more pizza, the economy needs to give up on two cakes
c. in order to produce one more cake, the economy needs to give up on half a pizza
d. none of the above is correct