Resources are being used efficiently when:

A) scarcity is no longer an issue.
B) they are also used equitably.
C) every opportunity to make people better off without making others worse off has been seized.
D) gains from trade are still available.

Efficiently Used

Utilized in a manner that maximizes productivity or effectiveness while minimizing waste or unnecessary expenditure of resources.

Scarcity

The fundamental economic problem of having seemingly unlimited human wants in a world of limited resources.