The production possibilities frontier curve illustrates that

a.an economy's capacity to produce is unrelated to its population.

b.if all the resources of an economy are being used efficiently,more of one good can be produced only if more of another good is produced.

c.an economy will automatically move toward a point at which all of its resources are being used inefficiently.

d.if all the resources of an economy are being used efficiently,more of one good can be produced only if less of another good is produced.