中等econ-u03-d03
Firm X's production creates pollution that third parties pay for. This negative externality means:
A. Social cost exceeds private cost, so an unregulated market overproduces✓ 答案
B. Social cost is below private cost, so the market underproduces
C. Social cost always equals private benefit
D. There is no gap between private and social cost
解說
Third parties bear part of the cost, so MSC > MPC and the market equilibrium quantity exceeds the socially efficient level. A per-unit tax equal to the external cost at the efficient quantity can close the gap.