大学英语六级分类模拟题382及答案解析.doc

1、大学英语六级分类模拟题 382及答案解析(总分：100.00，做题时间：90 分钟)一、Reading Comprehensio(总题数：0，分数：0.00)The recent, apparently successful prediction by mathematical models of an appearance of EI Ninothe warm ocean current that periodically develops along the Pacific coast of South Americahas excited researchers. Jacob Bjerk

2、nes pointed out over 20 years ago how winds might create either abnormally warm or abnormally cold water in the eastern equatorial Pacific. Nonetheless, until the development of the models no one could explain why conditions should regularly shift from one to the other, as happens in the periodic os

3、cillations between appearances of the warm EI Nino and the cold so-called anti-El Nino. The answer, at least if the current model that links the behavior of the ocean to that of the atmosphere is correct, is to be found in the ocean. It has long been known that during an El Nino, two conditions exis

4、t: unusually warm water extends along the eastern Pacific, principally along the coasts of Ecuador and Peru, and winds blow from the west into the warmer air rising over the warm water in the east. These winds tend to create a feedback mechanism by driving the warmer surface water into a “pile“ that

5、 blocks the normal upwelling of deeper, cold water in the east and further warms the eastern water, thus strengthening the wind still more. The contribution of the model is to show that the winds of an El Nino, which raise sea level in the cast, simultaneously send a signal to the west lowering sea

6、level. According to the model, that signal is generated as a negative Rossby wave, a wave of depressed, or negative, sea level, that moves westward parallel to the equator at 25 to 85 kilometers per day. Taking months to traverse the Pacific, Rossby waves march to the western boundary of the Pacific

7、 basin, which is modeled as a smooth wall but in reality consists of quite irregular island chains, such as, the Philippines and Indonesia. When the waves meet the western boundary, they are reflected, and the model predicts that Rossby waves will be broken into numerous coastal Kelvin waves carryin

8、g the same negative sea-level signal. These eventually shoot toward the equator, and then head eastward along the equator propelled by the rotation of the Earth at a speed of about 250 kilometers per day. When enough Kelvin waves of sufficient amplitude arrive from the western Pacific, their negativ

9、e sea-level signal overcomes the feedback mechanism tending to raise the sea level, and they begin to drive the system into the opposite cold mode. This produces a gradual shift in winds, one that will eventually send positive sea-level Rossby waves westward, waves that will eventually return as col

10、d cycle-ending positive Kelvin waves, beginning another warming cycle.（分数：20.00）(1).Which of the following best describes the organization of the first paragraph?（分数：4.00）A.A model is described and its value assessed.B.A result is reported and its importance explained.C.A phenomenon is noted and its

11、 significance debated.D.A hypothesis is introduced and contrary evidence presented.(2).According to the passage, which of the following features is characteristic of an El Nino?（分数：4.00）A.Cold coastal water near Peru.B.Wind blowing from the west.C.Random occurrence.D.Worldwide effects.(3).Which of t

12、he following, if true, would most seriously undermine the validity of the model El Nino that is presented in the passage?（分数：4.00）A.El Nino extends much farther along the coasts of Ecuador and Peru during some years.B.The rising of cold water in the eastern Pacific depends on the local characters.C.

13、The variations in the time for Rossby waves to cross the Pacific rely on the wind power.D.The Pacific irregular western coast hinders most Kelvin waves from heading eastward.(4).According to the model presented in the passage, which of the following normally signals the disappearance of an El Nino?（

14、分数：4.00）A.The arrival in the eastern Pacific of negative sea-level Kelvin waves.B.A shift in the direction of the winds produced by an anti-El Nino.C.The reflection of Kelvin waves reaching the eastern border of the Pacific.D.An increase in the speed at which negative Rossby waves cross the Pacific.

15、5).The primary purpose of the text as a whole is to _.（分数：4.00）A.introduce a new explanation of physical phenomenonB.explain the difference between two natural phenomenaC.illustrate the limits of applying mathematics to complex problemsD.clarify the distinction between an old explanation and a new

16、modelAided by the recent ability to analyze samples of air trapped in glaciers, scientists now have a clearer idea of the relationship between atmospheric composition and global temperature changing over the past 160,000 years. In particular, determination of atmospheric composition during periods o

17、f glacial expansion and retreat (cooling and warming) is possible using data from the 2,000 meter Vostok ice core drilled in Antarctica. The technique involved is similar to that used in analyzing cores of marine sediments, where the ratio of the two common isotopes of oxygen, 180 and 160, accuratel

18、y reflects past temperature changes. Isotopic analysis of oxygen in the Vostok core suggests mean global temperature fluctuations of up to 10 degrees centigrade over the past 160,000 years. Data from the Vostok core also indicate that the amount of carbon dioxide has fluctuated with temperature over

19、 the same period: the higher the temperature, the higher the concentration of carbon dioxide and the lower the temperature, the lower the concentration. Although change in carbon dioxide content closely follows change in temperature during periods of deglaciation, it apparently lags behind temperatu

20、re during periods of cooling. The correlation of carbon dioxide with temperature, of course, does not establish whether changes in atmospheric composition causing the warming and cooling trends or were caused by them. The correlation between carbon dioxide and temperature throughout the Vostok recor

21、d is consistent and predictable. The absolute temperature changes, however, are from 5 to 14 times greater than would be expected on the basis of carbon dioxide“s own ability to absorb infrared radiation, or radiant heat. This reaction suggests that, quite aside from changes in heat-trapping gases,

22、commonly known as greenhouse gases, certain positive feedbacks are also amplifying the temperature change. Such feedbacks might involve ice on land and sea, clouds, or water vapor, which also absorb radiant heat. Other data from the Vostok core show that methane gas also correlates closely with temp

23、erature and carbon dioxide. The methane concentration nearly doubled, for example, between the peak of the penultimate glacial period and the following interglacial period. Within the present interglacial period it has more than doubled in just the past 300 years and is rising rapidly. Although the

24、concentration of atmospheric methane is more than two orders of magnitude lower than that of carbon dioxide, it cannot be ignored: the radiative properties of methane make it 20 times more effective, molecule for molecule, than carbon dioxide in absorbing radiant heat. On the basis of a simulation m

25、odel that climatological researchers have developed, methane appears to have been about 25 percent as important as carbon dioxide in the warming that took place during the most recent glacial retreat 8,000 to 10,000 years ago.（分数：20.00）(1).The primary purpose of the passage is to _.（分数：4.00）A.interp

26、ret dataB.explain research methodologyC.evaluate a conclusionD.suggest a new technique(2).According to the passage, which of the following statements best describes the relationship between carbon dioxide and global temperature?（分数：4.00）A.Carbon dioxide levels change immediately in response to chang

27、es in temperature.B.Carbon dioxide levels correlate with global temperature during cooling periods only.C.During cooling periods, carbon dioxide levels initially remain high and then decline.D.Carbon dioxide levels increase more quickly than global temperature does.(3).The author mentions “certain p

28、ositive feedbacks“ (Line 6, Para.3) in order to indicate that（分数：4.00）A.increased concentration of carbon dioxide in the Earth“s atmosphere is responsible for global temperature increaseB.some climate simulation models have produced useful informationC.greenhouse gases alone do not account for globa

29、l temperature increaseD.variables that benefit life are causing global temperature to increase(4).According to the passage, which of the following statements about methane is true?（分数：4.00）A.Methane is found in marine sediments.B.Methane is more effective than carbon dioxide in absorbing radiant hea

30、t.C.The Earth“s atmosphere now contains more than twice as much methane as it does carbon dioxide.D.The higher the concentration of carbon dioxide in the Earth“s atmosphere, the lower the concentration of methane.(5).The passage suggests that when the methane concentration in the Earth“s atmosphere

31、decreases, which of the following also happens?（分数：4.00）A.Glaciers melt faster.B.The concentration of carbon dioxide increases.C.Carbon dioxide absorbs more radiant beat.D.The global temperature decreases.One of the simplest and best known kinds of crystal is the ionic salt, of which a typical examp

32、le is sodium chloride, or ordinary table salt. The fundamental components of an ionic salt are ions: atoms or molecules that have become electrically charged by gaining or losing one more electrons. In forming sodium chloride, for example, sodium atoms give up an electron (thereby becoming positivel

33、y charged) and chlorine atoms gain an electron (thereby becoming negatively charged). The ions are attracted to one another by their opposite charges, and they stack together compactly, like tightly packed spheres. Recently, scientists at Michigan State University created a new kind of crystal calle

34、d an electride. In electrides, the anions (negative ions) are completely replaced by electrons, which are trapped in naturally formed cavities within a framework of regularly stacked cations (positive ions). Electrides are the first examples of ionic salts in which all these anionic sites are occupi

35、ed solely by electrons. Unlike other types of anions, anionic electrons do not behave as if they were _simple charged spheres . In particular, because of their low mass and their tendency to interact with one another over great distances, they cannot be “pinned down“ to any one location. Instead, th

36、ey wander close to and among the atoms lining the cavity and interact with electrons in nearby cavities, perhaps changing places with them. The properties of an electride depend largely on the distance between the cavities that hold trapped electrons. When the trapped electrons are far apart, they d

37、o not interact strongly, and so behave somewhat like an array of isolated negative charges. When they are closer together, they begin to display properties associated with large ensembles of identical particles. When they are still closer, the ensemble properties dominate and the electrons “delocali

38、ze“: they are no longer tightly bound within individual cavities but are more or less flee to pass through the spaces within the framework of positive ions. By synthesizing electrides from a variety of materials, one can vary the geometry of the anionic cavities and their relation to the surrounding

39、 cations. The resulting properties may make it possible for electrides to become a basis for economically useful new materials and devices. For instance, because the electrons in some electrides are very weakly bound, these crystals could be effective as photosensitive detectors, in which an impingi

40、ng photon liberates an electron, resulting in a small electric current. The same weak binding could also make electrides useful in solar energy converters and as cathodes in batteries. One obstacle is the tendency of electrides to decompose through reaction with air and water. Researchers are seekin

41、g ways to increase their stability.（分数：20.00）(1).The text is primarily concerned with discussing _.（分数：4.00）A.a way to isolate electronsB.the characteristics of a new kind of crystalC.the structure of an ionic saltD.commercial uses for electrides(2).In the first paragraph, the author is primarily co

42、ncerned with _.（分数：4.00）A.introducing a variant on the standard atomic theoryB.describing how chlorine atoms can become negatively chargedC.providing background for the technical discussion to followD.describing some early research at Michigan State University(3).According to the text, the defining

43、characteristic of an electride is which of the following?（分数：4.00）A.Its positive is of particularly low mass.B.Its ions possess identical electrical charges.C.It contains a framework of regularly stacked ions.D.Its negative ions consist solely of electrons.(4).It can be inferred from the text that a

44、nions behaving as “simple charged spheres“ (Para.3) could be expected to _.（分数：4.00）A.readily lose electrons and become positively chargedB.move freely in and out of their cavitiesC.respond to photons by liberating electronsD.remain fixed relative to their cations(5).With which of the following stat

45、ements regarding electrides would the author most likely agree?（分数：4.00）A.They have proven themselves to be of great commercial value.B.Their future commercial value is promising but uncertain.C.They are interesting but of no practical value.D.They have commercial value mainly in solar energy applic

46、ations.Before 1965 many scientists pictured the circulation of the ocean“s water mass as consisting of large, slow-moving currents, such as the Gulf Stream. That view, based on 100 years of observations made around the globe, produced only a rough approximation of the true circulation. But in the 19

47、50“s and the 1960“s, researchers began to employ newly developed techniques and equipment, including subsurface floats that move with ocean currents and emit identification signals, and ocean current meters that record data for months at fixed locations in the ocean. These instruments disclosed an u

48、nexpected level of variability in the deep ocean. Rather than being characterized by smooth, large-scale currents that change seasonally (if at all), the seas are dominated by what oceanographers call mesoscale fields: fluctuating, energetic flows whose velocity can reach ten times the mean velocity

49、 of the major currents. Mesoscale phenomenathe oceanic analogue of weather systemsoften extend to distances of 100 kilometers and persist for 100 days (weather systems generally extend about 1,000 kilometers and last 3 to 5 days in any given area). More than 90 percent of the kinetic energy of the entire ocean may be accounted for by mesoscale variability rather than by large scale currents. Mesoscale phenomena may, in fact, play a significant role in oceanic mixing, air-sea interactions, and occasionalbut far-reachingclimatic events such as El Nino, the atmosphe