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　　逻辑结构题，从字面意思也很容易理解，就是要根据文章的逻辑结构来判断题干中的逻辑关系是否符合文章中的推理，在GMAT阅读中常常会出现一些虚拟语气或双重否定的情况，考生在遇到这类题目时一定要多加留意。逻辑题中经常会涉及到文章是如何构成的-例如，是通过定义，比较或对比来展现一个新观点或是反驳一个观点。作者是如何说服读者接受他的观点。作者使用一些特别的细节的原因。鉴定作者所使用的假设。评价作者论证的优缺点，识别出适当的反驳等。接下来小编将结合OG12的题目为大家详细介绍一下：

　　A recent study has provided clues to predator-prey dynamics in the late Pleistocene era. Researchers compared the number of tooth fractures in present-day carnivores with tooth fractures in carnivores that lived 36,000 to 10,000 years ago and that were preserved in the Rancho La Brea tar pits in Los Angeles. The breakage frequencies in the extinct species were strikingly higher than those in the present-day species.

　　In considering possible explanations for this finding, the researchers dismissed demographic bias because older individuals were not overrepresented in the fossil samples. They rejected preservational bias because a total absence of breakage in two extinct species demonstrated that the fractures were not the result of abrasion within the pits. They ruled out local bias because breakage data obtained from other Pleistocene sites were similar to the La Brea data. The explanation they consider most plausible is behavioral differences between extinct and present-day carnivores—in particular, more contact between the teeth of predators and the bones of prey due to more thorough consumption of carcasses by the extinct species. Such thorough carcass consumption implies to the researchers either that prey availability was low, at least seasonally, or that there was intense competition over kills and a high rate of carcass theft due to relatively high predator densities.

　　1. 分析文章结构

　　现象解释

　　2. 理清文章脉络

　　1) 第一段作文整篇文章的中心段，提出通过近期研究发现已灭绝动物种类牙齿断裂频率明显高于现存物种。

　　2) 第二段对为什么会出现这一现象的原因进行了分析，作者提到了三个存在但不正确的原因，最后提出了正确的原因。三个不正确原因分别为:

　　① the researchers dismissed demographic bias because older individuals were not overrepresented in the fossil samples.

　　② They rejected preservation bias because a total absence of breakage in two extinct species demonstrated that the fractures were not the result of abrasion within the pits.

　　③ They ruled out local bias because breakage data obtained from other Pleistocene sites were similar to the La Brea data.

　　正确原因：

　　The explanation they consider most plausible is behavioral differences between extinct and present-day carnivores--in particular, more contact between the teeth of predators and the bones of prey due to more thorough consumption of carcasses by the extinct species.

　　3. 问题解答

　　The researchers’ conclusion concerning the absence of demographic bias would be most seriously undermined if it were found that

　　(A) the older an individual carnivore is, the more likely it is to have a large number of tooth fractures

　　(B) the average age at death of a present-day carnivore is greater than was the average age at death of a Pleistocene carnivore

　　(C) in Pleistocene carnivore species, older individuals consumed carcasses as thoroughly as did younger individuals

　　(D) the methods used to determine animals’ ages in fossil samples tend to misidentify many older individuals as younger individuals

　　(E) data concerning the ages of fossil samples cannot provide reliable information about behavioral differences between extinct carnivores and present-day carnivores

　　题目分析：细节题目。

　　考点分析：该题属于逻辑结构中的削弱类，做逻辑削弱题的三个步骤：

　　i) 回文中定位处，找因果关系;

　　ii) 找原因反方向;

　　iii) 原因反方向即为正确选项。

　　注意，做逻辑削弱题，没必要挨个分析错误选项，只需迅速找到正确答案即可。以此题为例，按照解题三步骤，一步一步来选出正确选项。首先，根据题干中“demographic bias”,定位至第二段开头处的demographic bias. 找到因果关系词because. 然后，找寻因果反方向。文中说可以排除demographic bias的理由是老年个体没有在化石样本中过多出现。则咱们可以做出简单推理：如果老年个体在样本中过多出现了，则不能排除demographic bias. 最后，选到正确答案，应提到老年样本过多出现，(D)选项说把老年样本当作年轻样本算进去统计中了，也就是说老年样本过多出现，正确答案为D。

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