In a Two-Good Economy,the Production Possibilities Frontier (PPF)is

In a two-good economy,the production possibilities frontier (PPF) is

A) concave because the marginal rate of transformation increases as we move down the PPF.
B) concave because the marginal rate of transformation decreases as we move down the PPF.
C) convex because the marginal rate of transformation increases as we move down the PPF.
D) convex because the marginal rate of transformation decreases as we move down the PPF.
E) convex and the marginal rate of transformation is constant as move move down the PPF.