Production possibilities curves for large economies are generally bow-shaped because:

Production possibilities curves for large economies are generally bow-shaped because:
A.as more resources are used to produce a good, those resources become less expensive.
B.opportunity costs tend to increase with increases in production.
C.specialization gives some producers a comparative advantage.
D.opportunity costs tend to decrease with increases in production.
正确答案：opportunity costs tend to increase with increases in production.