On a graph of a production possibilities curve, if a point is attainable, then it:

On a graph of a production possibilities curve, if a point is attainable, then it:
A.is efficient only if it does not exhaust all currently available resources.
B.must be efficient.
C.might or might not be efficient.
D.must completely exhaust all currently available resources.
正确答案：might or might not be efficient.