1、大学英语六级改革适用（阅读）模拟试卷 53及答案与解析 Section C 0 One of the simplest and best known kinds of crystal is the ionic salt, of which a typical example 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 gain
2、ing or losing one more electrons. In forming sodium chloride, for example, sodium atoms give up an electron(thereby becoming positively 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 to
3、gether compactly, like tightly packed spheres. Recently, scientists at Michigan State University created a new kind of crystal called an electride. In electrides, the anions(negative ions)are completely replaced by electrons, which are trapped in naturally formed cavities within a framework of regul
4、arly stacked cations(positive ions). Electrides are the first examples of ionic salts in which all these anionic sites are occupied 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
5、their tendency to interact with one another over great distances, they cannot be “pinned down“ to any one location. Instead, they 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 de
6、pend largely on the distance between the cavities that hold trapped electrons. When the trapped electrons are far apart, they do 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 l
7、arge ensembles of identical particles. When they are still closer, the ensemble properties dominate and the electrons “delocalize“: they are no longer tightly bound within individual cavities but are more or less free to pass through the spaces within the framework of positive ions. By synthesizing
8、electrides from a variety of materials, one can vary the geometry of the anionic cavities and their relation to the surrounding 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 electro
9、ns in some electrides are very weakly bound, these crystals could be effective as photosensitive detectors, in which an impinging 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
10、 batteries. One obstacle is the tendency of electrides to decompose through reaction with air and water. Researchers are seeking ways to increase their stability. 1 The text is primarily concerned with discussing_. （ A） a way to isolate electrons （ B） the characteristics of a new kind of crystal （ C
11、） the structure of an ionic salt （ D） commercial uses for electrides 2 In the first paragraph, the author is primarily concerned with_. （ A） introducing a variant on the standard atomic theory （ B） describing how chlorine atoms can become negatively charged （ C） providing background for the technica
12、l discussion to follow （ D） describing some early research at Michigan State University 3 According to the text, the defining characteristic of an electride is which of the following? （ A） Its positive is of particularly low mass. （ B） Its ions possess identical electrical charges. （ C） It contains
13、a framework of regularly stacked ions. （ D） Its negative ions consist solely of electrons. 4 It can be inferred from the text that anions behaving as “simple charged spheres“(Para.3)could be expected to_. （ A） readily lose electrons and become positively charged （ B） move freely in and out of their
14、cavities （ C） respond to photons by liberating electrons （ D） remain fixed relative to their cations 5 With which of the following statements regarding electrides would the author most likely agree? （ A） They have proven themselves to be of great commercial value. （ B） Their future commercial value
15、is promising but uncertain. （ C） They are interesting but of no practical value. （ D） They have commercial value mainly in solar energy applications. 5 Before 1965 many scientists pictured the circulation of the oceans water mass as consisting of large, slow-moving currents, such as the Gulf Stream.
16、 That view, based on 100 years of observations made around the globe, produced only a rough approximation of the true circulation. But in the 1950s and the 1960s, researchers began to employ newly developed techniques and equipment, including subsurface floats that move with ocean currents and emit
17、identification signals, and ocean current meters that record data for months at fixed locations in the ocean. These instruments disclosed an unexpected level of variability in the deep ocean. Rather than being characterized by smooth, large-scale currents that change seasonally(if at all), the seas
18、are dominated by what oceanographers call mesoscale fields: fluctuating, energetic flows whose velocity can reach ten times the mean velocity of the major currents. Mesoscale phenomena the oceanic analogue of weather systems often extend to distances of 100 kilometers and persist for 100 days(weathe
19、r 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 oc
20、eanic mixing, air-sea interactions, and occasional but far-reaching climatic events such as El Nino, the atmospheric-oceanic disturbance in the equatorial Pacific that affects global weather patterns. Unfortunately, it is not feasible to use conventional techniques to measure mesoscale fields. To me
21、asure them properly, monitoring equipment would have to be laid out on a grid at intervals of at most 50 kilometers, with sensors at each grid point lowered deep in the ocean and kept there for many months. Because using these techniques would be prohibitively expensive and time consuming, it was pr
22、oposed in 1979 that tomography be adapted to measuring the physical properties of the ocean. In medical tomography X-rays map the human bodys density variations(and hence internal organs); the information from the X-rays, transmitted through the body along many different paths, is recombined to form
23、 three-dimensional images of the body s interior. It is primarily that this multiplicative increase in data obtained from the multipath transmission of signals that accounts for oceanographers attraction to tomography: it allows the measurement of vast areas with relatively few instruments. Research
24、ers reasoned that low-frequency sound waves, because they are so well described mathematically and because even small perturbations in emitted sound waves can be detected, could be transmitted through the ocean over many different paths and that the properties of the oceans interior its temperature,
25、 salinity, density, and speed of currents could be deduced on the basis of how the ocean altered the signals. Their initial trials were highly successful, and ocean acoustic tomography was born. 6 According to the passage, scientists are able to use ocean acoustic tomography to deduce the properties
26、 of the ocean s interior in part because_. （ A） density variations in the ocean are mathematically predictable （ B） mesoscale phenomena are so large as to be easily detectable （ C） information from sound waves can be recombined more easily than information from X-rays （ D） low-frequency sound waves
27、are well described mathematically 7 The author mentions EL Nino primarily in order to emphasize_. （ A） the difficulty of measuring the ocean s large scale currents （ B） the variability of mesoscale phenomena （ C） the brief duration of weather patterns （ D） the possible impact of mesoscale fields on
28、weather conditions 8 Which of the following is most similar to medical tomography as it is described in the passage? （ A） The use of earthquake shock-wave data collected at several different locations and combined to create a three-dimensional image of the Earth s interior. （ B） The use of ocean-cur
29、rent meters to determine the direction and velocity of the ocean s mesoscale fields. （ C） The use of a grid-point sensory system to map global weather patterns. （ D） The use of subsurface floats to map large-scale circulation in the ocean. 9 Which of the following best describes the organization of
30、the third paragraph of the passage? （ A） An argument is advanced, then refuted, and an alternative is suggested. （ B） Opposing views are presented, elaborated, and then reconciled. （ C） A problem is described, then a solution is discussed and its effectiveness is affirmed. （ D） A theory is proposed,
31、 considered and then amended. 10 Which of the following, if presented as the first sentence of a succeeding paragraph, would most logically continue the discussion presented in the passage? （ A） Ships are another possibility, but they would need to stop every 50 kilometers to lower measuring instrum
32、ents. （ B） To understand how ocean acoustic tomography works, it is necessary to know how sound travels in the ocean. （ C） Timekeeping in medical tomography must be precise because the changes in travel time caused by density fluctuations are slight. （ D） These variations amount to only about 2 to 3
33、 percent of the average speed of sound in water, which is about 1500 meters per second. 10 About a century ago, the Swedish physical scientist Arrhenius proposed a low of classical chemistry that relates chemical reaction rate to temperature. According to his equation, chemical reactions are increas
34、ingly unlikely to occur as temperature approaches absolute zero, and at absolute zero, reactions stop. However, recent experiment evidence reveals that although the Arrhenius equation is generally accurate in describing the kind of chemical reaction that occurs at relatively high temperature, at tem
35、peratures closer to zero a quantum-mechanical effect known as tunneling comes into play; this effect accounts for chemical reactions that are forbidden by me principles of classical chemistry. Specifically, entire molecules can tunnel through the barriers of repulsive forces from other molecules and
36、 chemically react even though these molecules do not have sufficient energy, according to classical chemistry, to overcome the repulsive barrier. The rate of any chemical reaction, regardless of the temperature at which it takes place, usually depends on a very important characteristic known as its
37、activation energy. Any molecule can be imagined to reside at the bottom of a so-called potential well of energy. A chemical reaction corresponds to the transition of a molecule from the bottom of one potential well to the bottom of another. In classical chemistry, such a transition can be accomplish
38、ed only by going over the potential barrier between the well, the height of which remains constant and is called the activation energy of the reaction. In tunneling, the reactings molecules tunnel from the bottom of one to the bottom of another well without having to rise over the barrier between th
39、e two wells. Recently researchers have developed the concept of tunneling temperature: the temperature below which tunneling transitions greatly outnumber Arrhenius transitions, and classical mechanics gives way to its quantum counterpart. This tunneling phenomenon at very low temperatures suggested
40、 my hypothesis about a cold prehistory of life: formation of rather complex organic molecules in the deep cold of outer space, where temperatures usually reach only a few degrees Kelvin. Cosmic rays might trigger the synthesis of simple molecules, such as interstellar formaldehyde, in dark clouds of
41、 interstellar dust. Afterward complex organic molecules would be formed, slowly but surely, by means of tunneling. After I offered my hypothesis, Hoyle and Wickramashinghe argued that molecules of interstellar formaldehyde have indeed evolved into stable polysaccharides such as cellulose and starch.
42、 Their conclusions, although strongly disputed, have generated excitement among investigators such as myself who are proposing that the galactic clouds are the places where the prebiological evolution of compounds necessary to life occurred. 11 According to the Arrhenius equations as discussed in th
43、e passage, which of the following statements about chemical reactions is true? （ A） Chemical reactions are less likely to occur at temperature close to absolute zero. （ B） In some cases the rate of a chemical reaction is related to temperature and in other cases it is not. （ C） The rate of a chemica
44、l reaction depends on many other factors besides temperature. （ D） Chemical reaction rate and temperature are not related. 12 In which of the following ways are the mentioned chemical reactions and tunneling reactions alike? （ A） In both types of reactions, reacting molecules have to rise over the b
45、arrier between the two wells. （ B） In both types of reactions, a transition is made from the bottom of one potential well to the bottom of another. （ C） In both types of reactions, reacting molecules are able to go through the barrier between the two wells. （ D） In neither type of reaction does the
46、rate of a chemical reaction depend on its activation energy. 13 Which of the following best describes the organization of the first two paragraphs of the passage? （ A） The author cites a basic principle of classical chemistry and then describes the research from which that principle was developed. （
47、 B） The author presents the fundamental rules of classical chemistry in order to introduce an explanation of a specific chemical reaction. （ C） The author describes the role of heat in chemical reactions and then offers a detailed explanation of its function. （ D） The author presents a law of classi
48、cal chemistry in order to introduce a kind of chemical reaction that differs from it and then explains the essential difference between the two. 14 Which of the following best describes the hypothesis of Hoyle and Wickramas-inghe? （ A） Molecules of interstellar formaldehyde can evolve into complex o
49、rganic molecules. （ B） Interstellar formaldehyde can be synthesized by tunneling. （ C） Cosmic rays can directly synthesize complex organic molecules. （ D） The galactic clouds are the places where prebiological evolution of compounds necessary to life occurred. 15 The author is mainly concerned with_. （ A） describing how the principles of classical chemistry were developed （ B） initiating a debate about the kinds of chemical reaction required for the development of life （ C） explaining how current research in chemistry may be related to broade
