On the Production Possibilities Frontier, the Opportunity Cost of Producing

On the production possibilities frontier, the opportunity cost of producing one more unit of a commodity per period is measured by the _____

A) monetary price of the commodity.
B) amount of the other commodity that must be sacrificed.
C) amount of unemployed resources that must be used.
D) amount of satisfaction it gives consumers.
E) amount of tax paid to the government for the production, sale, and use of the commodity.