单选题 Hardin argued that grazing land held in common (that is, open to any user) would always be used less carefully than private grazing land. Each rancher would be tempted to overuse common land because the benefits would accrue to the individual, while the costs of reduced land quality that results from overuse would be spread among all users. But a study comparing 217 million acres of common grazing land with 433 million acres of private grazing land showed that the common land was in better condition.
Which of the following, if true and known by the ranchers, would best help explain the results of the study?

A、 With private grazing land, both the costs and the benefits of overuse fall to the individual user
B、 The cost in reduced land quality that is attributable to any individual user is less easily measured with common land than it is with private land
C、 An individual who overuses common grazing land might be able to achieve higher returns than other users can, with the result that he or she would obtain a competitive advantage
D、 If one user of common land overuses it even slightly, the other users are likely to do so even more, with the consequence that the costs to each user outweigh the benefits
E、 There are more acres of grazing land held privately than there are held in common

【正确答案】 D

【答案解析】[解析] 该研究指出，公地比私人土地条件更好，正确答案(D)，指出与Hardin的宣称相反，不去过度使用公地是符合每个放牧者的自身利益的，这样来解释为什么公地有相对较好的条件；选项(A)和(C)只能解释为什么私人土地比公地条件更好，而不是相反；将公地条件恶化的成本分摊给每个使用者更加困难这一事实[选项(B)]和公地与私人土地相对量的不同这一事实[选项(E)]都没有给出一个理由来解释农场主们为什么尽可能地不在公地上牧养他们的牧群。