GRE阅读中的逻辑单题专门对学生的逻辑思维进行直接考查，我们GRE老师对这种文章已经给同学们做了比较多的介绍。但是这种逻辑单题却不是最典型的GRE阅读理解。GRE阅读中最典型、或者说GRE最小的单元是短文章（shorter passage），一般不到200个单词，后面跟两道题。按照官方的说法，短文章一般relatively straightforward and less dense（相对不那么复杂难懂）。所以对考生来说，多练习短文章，才能打好基础。今天我们就来看一篇2021年出现过的机经短文章。
01
Because they accumulate in an ordered manner that records changes within a lake and its drainage basin, lake sediments are particularly valuable for reconstructing ancient climate conditions. Natural materials such as pollen grains, minerals, diatoms, and animal microfossils preserved in sediments can be used to infer past conditions as these materials are affected by environmental variables. Pollen grains composed of sporopollenin, for example, can be used to infer past vegetation shifts. Because both natural climate change and human agricultural practices can lead to changes in vegetation, however, differentiation of these effects using pollen alone is difficult. In many areas of Mesoamerica, for instance, changes in the relative abundance of pollen types after 1000 BC were highly influenced by human-induced land clearance.
1. The author mentions “sporopollenin” primarily in order to
A. suggest that the conclusion set forth in the preceding sentence is overly general
B. support, by means of an illustration, an assertion made in the preceding sentence
C. introduce a concept for which a more specific example is given in the following sentence
D. identify a possible reason for the problem that is described in the following sentence
E. give an example that appears to contradict a principle set forth in the preceding sentence
Consider each of the choices separately and select all that apply.
2. Which of the following does the passage present as a reason that lake sediments are of particular value in the reconstruction of ancient climate conditions?
A. They allow scientists to distinguish between naturally occurring and human-induced vegetation changes.
B. They contain natural materials that are relatively unaffected by environmental variables during accumulation.
C. They collect over time in an ordered fashion.
02
文章大意：
湖底的沉积物是以一种有秩序的方式累积的，这种方式可以记录一个湖及其流域的历史变化情况。所以，要想重构古代气候的各种情况，湖底沉积物提供的信息尤其有价值。一些保存在湖底沉淀物中的天然物质，如花粉粒、矿物质、硅藻、动物的细微骸骨化石等，可以用来推断过去的天气状况，因为这些物质当年曾经受到过环境（气候）变量的影响。比如，包含sporopollenin（孢子花粉素，请同学们注意，这种单词不用背也不用学）成分的花粉粒，就可以被用来推测过去植被的变化情况。不过，因为天气变化和人类农业活动都会导致植被的变化，光用花粉这一种东西无法区分植被的变化到底是由天气变化导致还是人类农业活动导致。在中美洲的很多地区，在公元前1000年至今，（湖底沉积物中）花粉种类的数量的变化，就在很大程度上受到了人类伐木平整出空地这种活动的影响（不仅受气候变化的影响）。
题目解析：
1、 作者提到sporopollenin，主要的修辞目的是……？
作者提到sporopollenin，是讲包含sporopollenin成分的花粉粒，可以用来推测植被变化，进而推测气候变化情况。这是在用具体举例的方式支持文章上一句话做出的一个断言。文章上一句话说的是，一些天然物质（如花粉粒、矿物质、硅藻、动物化石等），可以用来推断过去的天气状况。这句话就具体说，花粉可以用来推断过去的植被变化情况（进而推断过去的天气变化状况）。简单地说，这句话是在illustrate上一句话。所以B选项正确。
2、 文章说，“要想重构古代气候的各种情况，湖底沉积物提供的信息尤其有价值”，文章提出的原因有哪些？
文章说了区别不出来天气变化和人类活动这两种因素引起的变化，所以A选项错误。B选项中说“unaffected by environmental variables”，而根据文章，正是因为湖底沉积物中的物质会受到气候条件的影响，它们才有用，有价值。所以B选项错误。
C选项中的collect是不及物动词，意思和文章第一句话中的accumulate接近。C选项中的fashion的意思和文章第一句话中的manner接近。所以C选项They collect over time in an ordered fashion 就和文章第一句话中的They accumulate in an ordered manner基本是对应的。所以C选项正确。
这篇文章到这里就讲解完了但是还想提醒同学们在GRE的题库里，一篇短文章可能有不只两道题，而是有4道题。每次考试，短文章后面是跟着两道题，但是不一定是哪两道。在两场考试中，文章是一样的，出现的题目却可能不一样。在一场考试中，会出现其中两道题；在另一场考试中，还是这篇文章，但出现的可能是另外两道题。
比如今天讲的这篇短文章，文章最后一句话，其实暗中表示了这样一层意思：
根据中美洲的很多地区公元前1000年至今（湖底沉积物中）花粉种类的数量的变化，无法准确推测公元前1000至今的气候变化情况，因为从公元前1000年起，人类的某些活动，也会影响花粉种类数量。
这最后一句话也是可以再出两道题的。比如，可以出这样一道问修辞目的的题目。
3. The author mentions “many areas of Mesoamerica” primarily in order to
A. suggest that the conclusion set forth in the preceding sentence is overly general
B. support, by means of an illustration, an assertion made in the preceding sentence
C. introduce a concept for which a more specific example is given in the following sentence
D. identify a possible reason for the problem that is described in the following sentence
E. give an example that appears to contradict a principle set forth in the preceding sentence
细心的同学一定注意到了。这道题的5个备选项和第1题一模一样，但是题干问的不是sporopollenin了，而是问的文章最后一句话中的many areas of Mesoamerica。那答案选哪个呢？
本期答案：B
还可以出这样一道推断题目。
4. Which of the following statements regarding many areas of Mesoamerica can be inferred from the passage？
A. 根据中美洲的很多地区公元前1000年至今（湖底沉积物中）动物化石的数量的变化，可以准确推测公元前1000至今的气候变化情况。
B. 中美洲很多地区公元前1000年至今（湖底沉积物中）花粉种类的数量的变化，受到人类活动影响的严重程度，比受到气候变化影响的严重程度，还要大。
C. 中美洲的很多地区公元前1000至今的湖底沉积物累积的方式，和其他地区不同。
D. 中美洲的很多地区公元前1000至今的气候变化的模式，和其他地区不同。
E. 仅仅根据中美洲的很多地区公元前1000年至今（湖底沉积物中）花粉种类的数量的变化，无法准确推测这些地区公元前1000至今的气候变化情况。
本期答案：E
03
临时返场：我们是2月12日写完这篇文章，交付排版。非常碰巧的是，我们在2月13日又得到了这篇文章的一道机经新题。
5. The author refers to “Mesoamerica” in the passage primarily in order to
A. describe an instance in which scientists were unable to determine the cause of a past vegetation shift
B. question the claim that both natural climate change and human agricultural practices may be responsible for past vegetation shifts
C. provide an example to support the contention that pollen grains are highly resistant to decay
D. support the contention that pollen changes captured in sediments do not reliably indicate natural climate change
E. identify a possible weakness in the theory that natural materials can be useful in inferring past climatic conditions
本期答案：D
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