When an Economy Is Operating Efficiently, the Production of One

When an economy is operating efficiently, the production of one more unit of a good will result in some loss of production of another good because:

A) technology can only improve the production of one good.
B) the production possibilities frontier (PPF) shifts inward as more of only one good is produced.
C) resources are limited and efficiency implies that all resources are already in use.
D) consumers will not want more of both goods.