Conservationbiologists have long been concerned thatspeciesextinctioncould havesignificantconsequences for thestabilityof entire ecosystems—groups of interacting organisms and thephysicalenvironment that theyinhabit. Anecosystemcouldsurvivethe loss of somespecies, but if enoughspecieswere lost, theecosystemwould beseverelydegraded. In fact, it is possible that the loss of a single importantspeciescould start acascadeof extinctions that mightdramaticallychange an entireecosystem. A goodillustrationof this occurred after sea otters were eliminated from somePacifickelp (seaweed) bed ecosystems: the kelp beds werepracticallyobliterated too because in theabsenceof seaotterpredation, seaurchinpopulations exploded and consumed most of the kelp and other macroalgae.

It is usually claimed that species-rich ecosystemstendto be morestablethan species-poor ecosystems. Three mechanisms by which higherdiversityincreasesecosystemstabilityhave been proposed. First, if there are morespeciesin anecosystem, then its food web will be morecomplex, with greater redundancy amongspeciesin terms of their nutritional roles. In other words, in a rich system if aspeciesis lost, there is a good chance that otherspecieswill take over itsfunctionasprey,predator, producer, decomposer, or whatever role it played. Second,diverseecosystems may be less likely to be invaded by newspecies,notablyexotics (foreignspeciesliving outside their native range), that woulddisrupttheecosystem’s structure andfunction. Third, in a species-richecosystem, diseases mayspreadmore slowly because mostspecieswill berelativelylessabundant, thus increasing theaveragedistance between individuals of the samespeciesand hamperingdiseasetransmission among individuals.

Scientificevidencetoilluminatethese ideas has been slow in coming, and many shadowsremain. One of the first studies to provide data supporting a relationship betweendiversityandstabilityexamined how grassland plants responded to adrought. Researchers D. Tilman and J A. Downing used theratioof above-ground biomass in 1988 (after two years ofdrought) to that in 1986 (predrought) in 207 plots in a grasslandfieldin the Cedar Creek NaturalHistoryArea in Minnesota as an index ofecosystemresponseto disruption bydrought. In an experiment that began in 1982, they compared these values with the number of plantspeciesin eachplotand discovered that the plots with a greater number of plantspeciesexperienced a lessdramaticreductionin biomass. Plots with more than tenspecieshad about half as much biomass in 1988 as in 1986, whereas those with fewer than fivespeciesonly producedroughlyone-eighth as much biomass after the two-yeardrought. Apparently, species-rich plots were likely tocontainsome drought-resistant plantspeciesthat grew better indroughtyears, compensating for the poor growth of less-tolerantspecies.

To put this result in more general terms, a species-richecosystemmay be morestablebecause it is more likely to havespecieswith a widearrayof responses tovariableconditions such as droughts. Furthermore, a species-richecosystemis more likely to havespecieswithsimilarecologicalfunctions, so that if aspeciesis lost from anecosystem, anotherspecies, probably a competitor, is likely toflourishandoccupyitsfunctionalrole. Both of these,variabilityin responses andfunctionalredundancy, could be thought of asinsuranceagainst disturbances.

The Minnesota grassland research has been widely accepted as strongevidencefor the diversity-stabilitytheory; however, its findings have been questioned, andsimilarstudies on other ecosystems have not always found apositiverelationship betweendiversityandstability. Clearly, this is acomplexissuethat requires furtherfieldresearch with abroadspectrumof ecosystems and species: grassland plants and computer models will only take us so far. In the end, despite insightful attempts todetectsome general patterns, we may find it very difficult to reduce this topic to a simple, universal truth.

Questions:
question_stem: The word "significant" in the passage is closest in meaning to
choices: tag: A
text: direct

tag: B
text: important

tag: C
text: long-term

tag: D
text: surprising
answer_key: B
explanation: 【题目翻译】文章中“significant”一词的意义最接近于以下哪个选项？
A：直接的
B：重要的
C：长期的
D：令人惊讶的

【判定题型】：题目要求选出与高亮单词意思最接近的选项，故判断本题为词汇题。

【关键词定位】：根据关键词“significant”,定位到原句“Conservation biologists have long been concerned that species extinction could have significant consequences for the stability of entire ecosystems—groups of interacting organisms and the physical environment that they inhabit. ”。

【词汇解析】：词汇“significant”的意思是“重要的”,带入到原句中，原句的意思是“长期以来，保护生物学家一直担心物种灭绝可能对整个生态系统——相互作用的有机体群和它们居住的物理环境的稳定性产生重大影响。”。

【选项分析】
A：直接的。不符，错误
B：重要的。与语境吻合，故为正确答案。
C：长期的。不符，错误
D：令人惊讶的。不符，错误

question_stem: According to paragraph 1, why has the extinction of species been a concern for conservation biologists?
choices: tag: A
text: When ecosystems lose just one species, they undergo permanent change.

tag: B
text: The extinction of a particular predator species could cause an overpopulation of certain prey species.

tag: C
text: The loss of one or more species could cause the decline of a whole ecosystem.

tag: D
text: The extinction of a single species is evidence that plant-food sources are in danger of disappearing.
answer_key: C
explanation: 【题目翻译】根据第1段，为什么物种灭绝一直是保护生物学家关注的问题？
A：当生态系统仅失去一种物种时，它们就会发生永久性的变化。

B：特定捕食性物种的灭绝可能导致某些猎物物种的过度繁殖。

C：一个或多个物种的损失可能导致整个生态系统的衰退。

D：单一物种的灭绝是植物食物源濒临消失的证据。

【判定题型】：题目问的是文章中的具体细节信息，故根据题目问法可以判断本题为事实信息题。

【关键词定位】：根据关键词“the extinction of species”,定位到 Passage 1 第2句，原句为“An ecosystem could survive the loss of some species, but if enough species were lost, the ecosystem would be severely degraded. @@@@In fact, it is possible that the loss of a single important species could start a cascade of extinctions that might dramatically change an entire ecosystem. ”。意思是“生态系统可以在某些物种的损失下存活，但是如果损失了足够的物种，生态系统将严重退化。事实上，单个重要物种的灭绝可能引发一系列的灭绝，从而可能显著地改变整个生态系统”。

【逻辑分析】找出物种灭绝的后果：就是单个重要物种的灭绝可能引发一系列的灭绝，从而可能显著地改变整个生态系统。

【选项分析】
A：“失去一种物种”不一定会导致生态永久的变化。错误。
B：B 选项是细节。错误。
C：与段落主题相符，正确。
D：物种灭绝不能直接和植物食物濒临消失直接挂钩。错误。

question_stem: According to paragraph 1, what was the result of the removal of Pacific sea otters?
choices: tag: A
text: The kelp and sea urchins were destroyed by new predators.

tag: B
text: The uncontrolled population of sea urchins ate most of the kelp plants.

tag: C
text: Without sea otters, the kelp beds soon became overgrown.

tag: D
text: Macroalgae remained as the primary population in the ecosystem.
answer_key: B
explanation: 【题目翻译】根据第1段，移除太平洋海獭的结果是什么？
A 海带和海胆被新的捕食者消灭了。

B 不受控制的海胆种群吃掉了大部分的海带植物。

C 没有海獭，海带床很快就长满了。

D 巨藻是生态系统的主要种群。

【判定题型】：题目问的是文章中的具体细节信息，故根据题目问法可以判断本题为事实信息题。

【关键词定位】：根据关键词“Pacific sea otters”,定位到 Passage 1 倒数第二句，原句为“A good illustration of this occurred after sea otters were eliminated from some Pacific kelp (seaweed) bed ecosystems: the kelp beds were practically obliterated too because in the absence of sea otter predation, sea urchin populations exploded and consumed most of the kelp and other macroalgae.”。意思是“海獭被从太平洋海藻（海草）床生态系统中移除就是一个很好的例子：没有了海獭捕食，海胆数量暴增，吃掉了大量海带和其他大型海藻，海草床也因此不复存在。”。

【逻辑分析】直接从定位句中找出两者之间的关系。移除太平洋海獭会导致海胆数量暴增，和海草床不复存在。

【选项分析】
A:海胆没有消失。故错误。
B:符合原文，正确。题干的 removal 对应这里的 absence。选项中的 uncontrolled 对应这里的 exploded。ate 对应句中的 consumed.
C:海草床消失了。故错误。
D:文章段落中并未提到巨藻是否是生态系统的主要种群。故错误。

question_stem: The word “redundancy” in the passage is closest in meaning to
choices: tag: A
text: duplication

tag: B
text: variety

tag: C
text: requirements

tag: D
text: flexibility
answer_key: A
explanation: 【题目翻译】文章中的“redundancy”一词最接近于
A:复制、副本
B:多样性
C:要求
D:灵活性

【判定题型】：题目要求选出与高亮单词意思最接近的选项，故判断本题为词汇题。

【关键词定位】根据关键词“redundancy”,定位到原句“Both of these, variability in responses and functional redundancy, could be thought of as insurance against disturbances.”。

【词汇解析】：词汇“redundancy”的意思是“复制”,带入到原句中，原句的意思是“这两者，响应的可变性和功能冗余，可以被认为是防止干扰的保险。”。

【选项分析】
A:复制、副本。与语境吻合，故为正确答案。
B:多样性。不符，错误
C:要求。不符，错误
D:灵活性。不符，错误

question_stem: What is the function of paragraph 2 in the passage?
choices: tag: A
text: To present a hypothesis about ecosystem diversity and some reasons why it might be true

tag: B
text: To give examples of types of ecosystems that have the greatest diversity

tag: C
text: To contradict a previous belief about the stability of species-rich ecosystems

tag: D
text: To contrast species-rich and species-poor ecosystems
answer_key: A
explanation: 【题目翻译】文章中第2段的作用是什么？

A：提出一个关于生态系统多样性的假说及其可能的原因。

B：举例说明具有最大多样性的生态系统类型。

C：与先前关于物种丰富生态系统稳定性的观点相矛盾。

D：对比物种丰富和物种贫乏的生态系统【判定题型】：根据题目问法，题目询问 xxx 组成或构成方式/段落与段落的关系/某一段在全文中所起的作用，故判断本题为组织结构题。

【内容分析】第二段先给出了一个 hypothesis: It is usually claimed that species-rich ecosystems tend to be more stable than species-poor ecosystems. 之后对这个 hypothesis 为什么正确给予了三种解释。

【选项分析】
A：正确。因为文章后面对这个 hypothesis 为什么正确给予了三种解释。
B：文章是提出的一个假设，而不是举例说明。故错误。
C：并不相矛盾，故错误。
D：文章没有进行对比，而是在提出假设。故错误。

question_stem: According to paragraph 2, which of the following increases the stability of an ecosystem?
choices: tag: A
text: Species in which producers outnumber predators

tag: B
text: New or exotic species that increase ecosystem diversity

tag: C
text: Heavily populated species that are free of disease

tag: D
text: Species that are diverse but have similar nutritional roles
answer_key: D
explanation: 【题目翻译】根据第2段，下列哪一项提高了生态系统的稳定性？

A：生产者数量超过捕食者的物种

B：增加生态系统多样性的新物种或外来物种

C：人口稠密的无病物种

D：种类繁多，但营养作用相似

【判定题型】：题目问的是文章中的具体细节信息，故根据题目问法可以判断本题为事实信息题。

【关键词定位】：根据关键词“stability”,定位到 Passage 2第3句，原句为“First, if there are more species in an ecosystem, then its food web will be more complex, with greater redundancy among species in terms of their nutritional roles. ”，意思是“首先，如果一个生态系统中有更多的物种，那么它的食物网将更加复杂，物种之间在营养作用方面具有更大的冗余性。”。

【逻辑分析】段落一共提出了3点：1、在一个物种丰富的系统里，如果失去了一个物种，就给了其它物种一个很好的机会，代替它扮演猎物、捕食者、生产者、分解者、或任何它所扮演的角色。2、多样的生态系统不太可能遭到新物种的入侵。3、疾病可能会传播得比较慢。

【选项分析】
A：不符文意，错误
B：不符文意，错误
C：不符文意，错误
D：符合文意，正确

question_stem: Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
choices: tag: A
text: In any ecosystem, as the number of individuals in the same species increases, the rate of disease transmission slows down.

tag: B
text: Ecosystems that have a small number of different species tend to be disease-free, because the species’ habitats are at a safe distance from each other.

tag: C
text: In ecosystems with many species, diseases spread more slowly because there are fewer individuals in a species and, as a result, the individuals are more widely scattered.

tag: D
text: The average distance between individuals in a species-rich ecosystem increases, so diseases are prevented from being communicated between species.
answer_key: C
explanation: 【题目翻译】下面哪个句子最能表达文章中突出句子的基本信息？不正确的选择会以重要方式改变含义，或者漏掉必要的信息。
A：在任何生态系统中，随着同一物种中个体数量的增加，疾病传播速度减慢。

B：只有少量不同物种的生态系统趋向于无病，因为物种的栖息地彼此之间处于安全距离。

C：在许多物种的生态系统中，疾病传播较慢，因为一个物种的个体较少，因此个体分布较广。

D：在物种丰富的生态系统中，个体之间的平均距离增加，因此疾病被防止在物种之间传播。

【判定题型】：根据题目问法，题目要求选择和高亮句意思逻辑都最为接近的句子，故判断本题为句子简化题。

【句子分析】？？？原句的逻辑为因果逻辑，因为句中出现了 because. 句子的核心为： Diseases may spread more slowly, thus increasing distance and hampering disease transmission.
意思是：疾病可能传播得更慢，从而增加距离并阻碍疾病传播。

【选项分析】
A：是不同物种的数量增加。不是同一物种。故错误。
B；文章是说：在一个物种丰富的生态系统中，疾病可能会传播得比较慢，因为每个物种的数量相对较少，从而增加了同一物种内个体间的平均距离，从而阻碍了个体间的疾病传播。故错误。
C：其核心与原句吻合，且逻辑关系一致。符合文意，正确。
D：是同一物种内个体的平均距离。D 选项中没有加“相同物种”，只说了个体间。故错误。

question_stem: The phrase ”compensating for" in the passage is closest in meaning to
choices: tag: A
text: working against

tag: B
text: leaving out

tag: C
text: making up for

tag: D
text: spreading over
answer_key: C
explanation: 【题目翻译】文章中“compensating for”这个短语的意思最接近于
A 反对
B 省略
C 弥补
D 遍布于

【判定题型】：题目要求选出与高亮单词意思最接近的选项，故判断本题为词汇题。

【关键词定位】：根据关键词“compensating for”,定位到原句“Apparently, species-rich plots were likely to contain some drought-resistant plant species that grew better in drought years, compensating for the poor growth of less-tolerant species.”。

【词汇解析】：词汇“compensating for”的意思是“弥补”,带入到原句中，原句的意思是“显然，物种丰富的地块可能包含一些抗旱的植物物种，这些物种在干旱年份生长得更好，弥补了耐旱性较差的物种生长不良。”。

【选项分析】
A 反对。不符，错误
B 省略。不符，错误
C 弥补。同义替换，为正确选项。
D 遍布于。不符，错误

question_stem: What is the main importance of the study discussed in paragraph 3?
choices: tag: A
text: It examines the response of certain grassland plants to a drought.

tag: B
text: It contains an index of plants that survived well in times of drought.

tag: C
text: It provides scientific evidence that diversity helps to make ecosystems stable.

tag: D
text: It shows that ecosystems contain both resistant species and less tolerant ones.
answer_key: C
explanation: 【题目翻译】第3段所讨论的研究的主要重要性是什么？
A：它检测某些草原植物对干旱的反应。

B：它包含干旱时期存活良好的植物的指数。

C：这提供了科学证据表明多样性有助于使生态系统稳定。

D：这表明生态系统中既有抗性物种，也有耐性较弱的物种。

【判定题型】：根据题目问法，题目询问 xxx 组成或构成方式/段落与段落的关系/某一段在全文中所起的作用，故判断本题为组织结构题。

【内容分析】第三段的中心句为段落最后一句：Apparently, species-rich plots were likely to contain some drought-resistant plant species that grew better in drought years, compensating for the poor growth of less-tolerant species.意思是：显然，物种丰富的地块很可能包含一些抗旱植物品种，这些品种在干旱年份生长得更好，弥补了那些不那么抗旱的品种的数量。而段落前面主要讲了相关的 research。表明了重要性是：物种丰富有利于生态系统稳定。

【选项分析】
A：不符，错误
B：不符，错误
C：表明了重要性是：物种丰富有利于生态系统稳定。符合，正确。
D：不符，错误

question_stem: The word “detect” in the passage is closest in meaning to
choices: tag: A
text: repeat

tag: B
text: alter

tag: C
text: find

tag: D
text: emphasize
answer_key: C
explanation: 【题目翻译】文章中“detect”这个词的意思最接近于
A:重复
B:改变
C:找寻、找到
D:强调

【判定题型】：题目要求选出与高亮单词意思最接近的选项，故判断本题为词汇题。

【关键词定位】：根据关键词“detect”,定位到原句“In the end, despite insightful attempts to detect some general patterns, we may find it very difficult to reduce this topic to a simple, universal truth.
”。
【词汇解析】：词汇“detect”的意思是“探测、发现”,带入到原句中，原句的意思是“最后，尽管有洞察力地试图检测一些一般模式，我们可能发现很难将这个主题简化为一个简单的、普遍的真理。”。

【选项分析】
A:重复。不符，错误
B:改变。不符，错误
C:找寻、找到。同义替换，正确
D:强调。不符，错误

question_stem: According to paragraph 5, which of the following is true about Tilman and Downing’s findings?
choices: tag: A
text: General patterns of diversity and stability have been established as a result of the findings.

tag: B
text: Questions about the findings have been refuted by computer models.

tag: C
text: The findings have been tested in a broad spectrum of ecosystems with similar results.

tag: D
text: The findings are not sufficient to prove a definite link between diversity and stability in ecosystems.
answer_key: D
explanation: 【题目翻译】根据第5段，关于 Tilman 和 Downing 的发现，以下哪个是正确的？
A：调查结果建立了多样性和稳定性的一般模式。

B：关于这些发现的问题被计算机模型驳倒了。

C：这一发现已经在广泛的生态系统中进行了测试，结果也类似。

D：这些发现不足以证明生态系统多样性和稳定性之间的明确联系。

【判定题型】：题目问的是文章中的具体细节信息，故根据题目问法可以判断本题为事实信息题。

【关键词定位】：根据关键词“Tilman and Downing’s findings”直接定位到 Passage 5。意思是：明尼苏达草原的研究作为多样性-稳定性理论的有力证据已被广泛接受，但是，它的研究结果已经被质疑，另外其他生态系统的类似的研究并没有找到多样性和稳定性之间积极的相关性。显然，这是一个复杂的问题，需要进一步的关于更多各种生态系统和物种的实地研究，对草地的研究和建立计算机模型只能证明部分问题。最后，尽管这些富有洞察力的尝试得出了一些概括性结论，我们可能会发现很难将这个话题缩小成一个简单的、普遍认可的事实。

【逻辑分析】：结合题目问法和出题句，进行逻辑分析。

【选项分析】
A:文章说研究结果已经被质疑了。故错误。
B:文章未说其有没有被驳倒。故错误。
C:文章未说有没有进行测试。故错误。
D:与原文意思相符，正确。