The Production Possibilities Frontier Is

The production possibilities frontier is

A) upward sloping and illustrates a tradeoff in production of the good measured on the x-axis and the good measured on the y-axis.
B) downward sloping and illustrates a tradeoff in production of the good measured on the x-axis and the good measured on the y-axis.
C) upward sloping and a movement along the PPF illustrates a free lunch.
D) downward sloping and a movement along the PPF illustrates a free lunch.
E) downward sloping and illustrates the marginal benefit from increasing production of the good measured on the x-axis.