基本分析：

原文选自李奥帕德的《沙郡岁月：李奥帕德的自然沉思》，本书是环保生态的经典著作，中译本由吴美真翻译，中国社会科学出版社出版。

以下是我做的一个初译稿，时间仓促，有误的话，请指出。

后面我有详细的分析。

46）Ornithologists (出题人改为：Scientists) jumped to the rescue with some distinctly shaky evidence to the effect that insects would eat us up if birds failed to control them.

科学家们迅速赶来救援，他们使用的证据明显站不住脚，大意是说：如果鸟不能控制这些虫子，虫子就会吃光一切。

47）but we have at least drawn nearer point of admitting that birds should continue as a matter of biotic（出题人应该把biotic“生物的” 改为了intrinsic“固有的，内在的”） right, regardless of the presence or absence of economic advantage to us.

但是我们起码得到了一种比较相近的观点，即：承认鸟类应该继续享有其固有的生物权利，而不管它们是否对我们具有经济价值。

48）Time was when biologists somewhat overworked the evidence that these creatures preserve the health of game by killing weaklings（出题人把这个词改为the physically weak）, or that they control rodents for the farmer(出题人应该把这句删除了), or that they prey only on worthless' species.

有一种证据认为，这些生物通过猎杀弱者来保存猎物的健康繁衍，或者这些生物捕杀的只不过是毫无意义的物种；曾几何时，生物学家有点滥用这种证据。

49）In Europe, where forestry is ecologically more advanced, the non-commercial tree species are recognized as members of the native forest community, to be preserved as such, within reason. 在欧洲，其林业在生态上更加发达，公益林木被认为是原始森林群落的一部分，本身应该得到合理保护。

50）It tends to ignore, and thus eventually to eliminate, many elements in the land community that lack commercial value, but that are (as far as we know)（命题人把原文括号部分删除了） essential to its healthy functioning. 我们很容易忽视，因而最终会淘汰土地群体里的很多重要因素，虽然这些要素缺乏商业价值，但他们对土地的健康机制却至关重要。