Answer: c). according to the ppf, as we produce more of one product, eventually we have give up more and more of the other product.
Explanation: PPF shows all possible combination of goods that a country can produce with its limited resources. The slope of a PPF is the opportunity cost which shows the units of goods that must be sacrificed to gain more and more units of the other good. As we move down the PPF the opportunity cost increases. This means that more and more units of a good must be sacrificed to gain additional units of the other good.