OG-86 解释题答案的标准

OG-86.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.>>

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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.

The study indicates that common lands are in better shape than private lands. The best answer, D, indicates that, contrary to Hardin’s claim, it is in each rancher’s self-interest not to overuse common land, which would explain why common lands are in relatively good shape.

我觉得答案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.  的解释作用不是很理解

OG解释中说是self interest，但D只是表述的一个客观事实，并没有说使用common land的人知道这个客观事实，那如何能说是each rancher’s self interest呢？

个人觉得，D对实际的情况的解释并不充分，充分的解释应该是：use common land 的大部分人知道“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.” 这样一个事实

由此我就对解释题答案的标准产生了一点疑惑，怎样才算是进行了解释呢？请NN解惑