A production possibilities frontier​ (PPF) is
A. a curve showing the maximum attainable combinations of two products that may be produced with available resources and current technology.
B. a curve that shows the potential productive capabilities of the frontier​ (defined as the area outside of​ cities) of a developing economy.
C. a curve that illustrates the demand of two goods for the average consumer.
D. a curve showing the generally attainable combinations of two products that may be produced with all planned or​ potential, yet undeveloped technology.