The Concave Shape of a Production Possibilities Frontier Showing Possible

The concave shape of a production possibilities frontier showing possible output levels of good A and good B indicates that if the economy produces more and more of good B,

A) larger and larger amounts of good A must be sacrificed
B) smaller and smaller amounts of good A must be sacrificed
C) more of good A will be produced
D) the amount of resources available in the economy must be increased
E) there must be an improvement in technology