46.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
参考译文：科学家们赶紧拿出某些明显站不住脚的证据前来救驾，大致说的是如果鸟儿不能控制害虫的话，害虫就会把我们吃掉。
1.句子的主干是“scientists jumped to the rescue with some distinctly shaky evidence”. 后接that 引导的同位语从句。 “to the effect ”是“大致意思是，大概是说的意思 ”。

2.句子结构整体不难，但隐藏着一些有难度的单词和短语，比如“jump to the rescue, distinct， shaky。

3. 此句难度不大

47.But we have at least drawn nearer the point of admitting that birds should continue as a matter of intrinsic right, regardless of the presence or absence of ecnomic advantage to us
参考译文：但是我们至少已经几乎承认了这样一种观点：那就是鸟儿的生存是它们的固有权利，不管它对我们是否有经济利益。

1. 句子整体结构是一个that引导的宾语从句。

2. 句子整体结构相对简单。

48.Time was when biologists somewhat over-worked the evidence that these creatures preserve the health of game by killing the physically weak, or that they prey only on "worthless" species

参考译文：曾几何时，生物学家总是重述以下的这条证据：这些生物是为了维持食物链的正常运行去捕食弱小的生物或“没有价值的物种”。
1.需要注意的是Time was when，应翻译成曾几何时，是一个固定搭配。

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
参考译文：在生态林业较为先进的欧洲，没有成为商业化对象的树种被视为原始森林群落的成员适当地加以保护。

1. 句子的主干是“the noncommercial tree species are recognized as members of the native forest community”，是一个被动语态。句子开头是一个where引导的定语从句，to be preserved是修饰noncommercial tree species的成分。

2. 需要注意的是within reason和native forest community，是两个固定搭配

3. 此句结构不难，但分析起来比较复杂。

50.It tends to ignore, and thus eventually to eliminate, many elements in the land community that lack commercial value, but that are essential to its healthy functioning
参考译文：他容易忽视并最终消灭很多缺乏商业价值的物种，然而这些物种对于整个生物群落的健康运行是至关重要的。

1. 句子的主干很简单，即“it tends to ignore and eliminate many elements”. 后接that引导的两个定语从句，但先行词都是elements。翻译时可先将主干翻译出来，然后将第一个定于从句嵌在主干中，but后的定语从句分开翻译。

2.这句话翻译起来相对简单，结构不复杂。