The Concept of Opportunity Cost

The concept of opportunity cost

A) cannot be explained by using a production possibilities frontier.
B) explains that goods are swapped for other goods.
C) implies that when a person is more efficient in the production of one good, he should produce that good and exchange it for some good that he is relatively less efficient at producing.
D) implies that a double coincidence of wants must be present for exchange to take place.
E) implies that because productive resources are scarce, we must give up some of one good to acquire more of another.