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Passage 26
  In choosing a method for determining climatic condi-tions that existed in the past, paleoclimatologists invokefour principal criteria1. First, the material——rocks, lakes,vegetation, etc-on which the method relies must be(5) widespread enough to provide plenty of information,since analysis of material that is rarely encountered willnot permit correlation2 with other regions or with otherperiods of geological history. Second, in the process offormation, the material must have received an environ-(10) mental signal that reflects a change in climate and thatcan be deciphered by modern physical or chemicalmeans. Third, at least some of the material must haveretained the signal unaffected by subsequent changes inthe environment. Fourth, it must be possible to deter-(15) mine the time at which the inferred climatic conditionsheld. This last criterion is more easily met in datingmarine sediments4, because dating of only a smallnumber of layers in a marine3 sequence allows the age ofother layers to be estimated fairly reliably by extrapola-(20) tion and interpolation. By contrast, because sedimenta-tion is much less continuous in continental5 regions, esti-mating the age of a continental bed from the knownages of beds above and below is more risky6.
  One very old method used in the investigation7 of past(25) climatic conditions involves the measurement of waterlevels in ancient lakes. In temperate8 regions, there areenough lakes for correlations9 between them to give us areliable picture. In arid10 and semiarid11 regions, on theother hand, the small number of lakes and the great(30) distances between them reduce the possibilities for corre-lation. Moreover, since lake levels are controlled by ratesof evaporation12 as well as by precipitation, the interpreta-tion of such levels is ambiguous. For instance, the factthat lake levels in the semiarid southwestern United(35) States appear to have been higher during the last ice agethan they are now was at one time attributed toincreased precipitation. On the basis of snow-line eleva-tions, however, it has been concluded that the climatethen was not necessarily wetter than it is now, but rather(40) that both summers and winters were cooler, resulting in  reduced evaporation.
  Another problematic method is to reconstruct formerclimates on the basis of pollen13 profiles. The type of vege-tation in a specific region is determined14 by identifying(45) and counting the various pollen grains found there.Although the relationship between vegetation andclimate is not as direct as the relationship betweenclimate and lake levels, the method often works well inthe temperate zones. In arid and semiarid regions in(50) which there is not much vegetation, however, smallchanges in one or a few plant types can change thepicture dramatically, making accurate correlations  between neighboring areas difficult to obtain.

  1. Which of the following statements about the difference between marine and continental sedimentation15 is supported by information in the passage?
   (A) Data provided by dating marine sedimentation is more consistent with researchers‘ findings in other disciplines than is data provided by dating continental sedimentation.
   (B) It is easier to estimate the age of a layer in a sequence of continental sedimentation than it is to estimate the age of a layer in a sequence of marine sedimentation.
   (C) Marine sedimentation is much less widespread than continental sedimentation.
   (D) Researchers are more often forced to rely on extrapolation when dating a layer of marine sedimentation than when dating a layer of continental sedimentation.
   (E) Marine sedimentation is much more continuous than is continental sedimentation.

  2. Which of the following statements best describes the organization of the passage as a whole?
   (A) The author describes a method for determining past climatic conditions and then offers specific examples of situations in which it has been used.
   (B) The author discusses the method of dating marine and continental sequences and then explains how dating is more difficult with lake levels than with pollen profiles.
   (C) The author describes the common requirements of methods for determining past climatic conditions and then discusses examples of such methods.
   (D) The author describes various ways of choosing a material for determining past climatic conditions and then discusses how two such methods have yielded contradictory16 data.
   (E) The author describes how methods for determining past climatic conditions were first developed and then describes two of the earliest known methods.

  3. It can be inferred from the passage that paleoclimatologists have concluded which of the following on the basis of their study of snow-line elevations17 in the southwestern United States?
   (A) There is usually more precipitation during an ice age because of increased amounts of evaporation.
   (B) There was less precipitation during the last ice age than there is today.
   (C) Lake levels in the semiarid southwestern United States were lower during the last ice age than they are today.
   (D) During the last ice age, cooler weather led to lower lake levels than paleoclimatologists had previously18 assumed.
   (E) The high lake levels during the last ice age may have been a result of less evaporation rather than more precipitation.

  4. Which of the following would be the most likely topic for a paragraph that logically continues the passage?
   (A) The kinds of plants normally found in arid regions
   (B) The effect of variation in lake levels on pollen distribution
   (C) The material best suited to preserving signals of climatic changes
   (D) Other criteria invoked19 by paleoclimatologists when choosing a method to determine past climatic conditions
   (E) A third method for investigating past climatic conditions

  5. The author discusses lake levels in the southwestern United States in order to
   (A) illustrate20 the mechanics of the relationship between lake level, evaporation, and precipitation
   (B) provide an example of the uncertainty21 involved in interpreting lake levels
   (C) prove that there are not enough ancient lakes with which to make accurate correlations
   (D) explain the effects of increased rates of evaporation on levels of precipitation
   (E) suggest that snow-line elevations are invariably more accurate than lake levels in determining rates of precipitation at various points in the past

  6. It can be inferred from the passage that an environmental signal found in geological material would not be useful to paleoclimatologists if it
   (A) had to be interpreted by modern chemical means
   (B) reflected a change in climate rather than a long-term climatic condition
   (C) was incorporated into a material as the material was forming
   (D) also reflected subsequent environmental changes
   (E) was contained in a continental rather than a marine sequence

  7. According to the passage, the material used to determine past climatic conditions must be widespread for which of the following reasons?
   Ⅰ.Paleoclimatologists need to make comparisons between periods of geological history.
   Ⅱ. Paleoclimatologists need to compare materials that have supported a wide variety of vegetation.
   Ⅲ. Paleoclimatologists need to make comparisons with data collected in other regions. 
   (A) Ⅰ only
   (B) Ⅱ only
   (C) Ⅰ and Ⅱ only
   (D) Ⅰ and Ⅲ only
   (E) Ⅱ and Ⅲ only

  8. Which of the following can be inferred from the passage about the study of past climates in arid and semiarid regions?
   (A) It is sometimes more difficult to determine pastclimatic conditions in arid and semiarid regions thanin temperate regions.
   (B) Although in the past more research has been done on temperate regions, paleoclimatologists have recently turned their attention to arid and semiarid regions.
   (C) Although more information about past climates can be gathered in arid and semiarid than in temperate regions, dating this information is more difficult.
   (D) It is difficult to study the climatic history of arid and semiarid regions because their climates have tended to vary more than those of temperate regions.
   (E) The study of past climates in arid and semiarid regions has been neglected because temperate regions support a greater variety of plant and animal life.


1 criteria vafyC     
  • The main criterion is value for money.主要的标准是钱要用得划算。
  • There are strict criteria for inclusion in the competition.参赛的标准很严格。
2 correlation Rogzg     
  • The second group of measurements had a high correlation with the first.第二组测量数据与第一组高度相关。
  • A high correlation exists in America between education and economic position.教育和经济地位在美国有极密切的关系。
3 marine 77Izo     
  • Marine creatures are those which live in the sea. 海洋生物是生存在海里的生物。
  • When the war broke out,he volunteered for the Marine Corps.战争爆发时,他自愿参加了海军陆战队。
4 sediments 8b3acb612b624abdf2c2881bc6928565     
沉淀物( sediment的名词复数 ); 沉积物
  • When deposited, 70-80% of the volume of muddy sediments may be water. 泥质沉积物沉积后,体积的70-80%是水。
  • Oligocene erosion had truncated the sediments draped over the dome. 覆盖于穹丘上的沉积岩为渐新世侵蚀所截削。
5 continental Zazyk     
  • A continental climate is different from an insular one.大陆性气候不同于岛屿气候。
  • The most ancient parts of the continental crust are 4000 million years old.大陆地壳最古老的部分有40亿年历史。
6 risky IXVxe     
  • It may be risky but we will chance it anyhow.这可能有危险,但我们无论如何要冒一冒险。
  • He is well aware how risky this investment is.他心里对这项投资的风险十分清楚。
7 investigation MRKzq     
  • In an investigation,a new fact became known, which told against him.在调查中新发现了一件对他不利的事实。
  • He drew the conclusion by building on his own investigation.他根据自己的调查研究作出结论。
8 temperate tIhzd     
  • Asia extends across the frigid,temperate and tropical zones.亚洲地跨寒、温、热三带。
  • Great Britain has a temperate climate.英国气候温和。
9 correlations 4a9b6fe1ddc2671881c9aa3d6cc07e8e     
相互的关系( correlation的名词复数 )
  • One would expect strong and positive correlations between both complexes. 人们往往以为这两个综合体之间有紧密的正相关。
  • The correlations are of unequal value. 这些对应联系的价值并不相同。
10 arid JejyB     
  • These trees will shield off arid winds and protect the fields.这些树能挡住旱风,保护农田。
  • There are serious problems of land degradation in some arid zones.在一些干旱地带存在严重的土地退化问题。
11 semiarid oiozuX     
  • The region is semiarid to arid in overall climate.这个地区总体上是半干旱至干旱气候。
  • In many semiarid areas there is also a lower timberline where the forest passes into steppe or desert at its lower edge,usually because of a lack of moisture.在很多半干旱地带也有下层的树带界限,在这种环境中,由于缺乏水分,森林下缘逐渐变成干草原或者是沙漠。
12 evaporation Pnoxc     
  • Be careful not to lose too much liquid by evaporation.小心不要因蒸发失去太多水分。
  • Our bodies can sweat,thereby losing heat by evaporation.我们的身体能出汗,由此可以蒸发散热。
13 pollen h1Uzz     
  • Hummingbirds have discovered that nectar and pollen are very nutritious.蜂鸟发现花蜜和花粉是很有营养的。
  • He developed an allergy to pollen.他对花粉过敏。
14 determined duszmP     
  • I have determined on going to Tibet after graduation.我已决定毕业后去西藏。
  • He determined to view the rooms behind the office.他决定查看一下办公室后面的房间。
15 sedimentation msEyJ     
  • Sedimentation, the damage of a breach are problems, too. 而且沉积和决口的问题,也是存在的。 来自英语晨读30分(高二)
  • Sedimentation and denudation play a role in exceptional cases. 沉积和剥蚀作用的影响只在特殊情况下起作用。
16 contradictory VpazV     
  • The argument is internally contradictory.论据本身自相矛盾。
  • What he said was self-contradictory.他讲话前后不符。
17 elevations cb4bbe1b6e824c996fd92d711884a9f2     
(水平或数量)提高( elevation的名词复数 ); 高地; 海拔; 提升
  • Weight of the crust changes as elevations are eroded and materials are deposited elsewhere. 当高地受到侵蚀,物质沉积到别的地方时,地壳的重量就改变。
  • All deck elevations are on the top of structural beams. 所有甲板标高线均指结构梁顶线。
18 previously bkzzzC     
  • The bicycle tyre blew out at a previously damaged point.自行车胎在以前损坏过的地方又爆开了。
  • Let me digress for a moment and explain what had happened previously.让我岔开一会儿,解释原先发生了什么。
19 invoked fabb19b279de1e206fa6d493923723ba     
v.援引( invoke的过去式和过去分词 );行使(权利等);祈求救助;恳求
  • It is unlikely that libel laws will be invoked. 不大可能诉诸诽谤法。
  • She had invoked the law in her own defence. 她援引法律为自己辩护。 来自《简明英汉词典》
20 illustrate IaRxw     
  • The company's bank statements illustrate its success.这家公司的银行报表说明了它的成功。
  • This diagram will illustrate what I mean.这个图表可说明我的意思。
21 uncertainty NlFwK     
  • Her comments will add to the uncertainty of the situation.她的批评将会使局势更加不稳定。
  • After six weeks of uncertainty,the strain was beginning to take its toll.6个星期的忐忑不安后,压力开始产生影响了。