gre考试阅读真题解析(A)

　　National character is not formally considered by social scientists in discussing economic and social development today. They believe that people differ and that these differences should be taken into account somehow, but they have as yet discovered no way to include such variables in their formal models of economic and social development. The difficulty lies in the nature of the data that supposedly define different national characters. Anthropologists and others are on much firmer ground when they attempt to describe the cultural norms for a small homogeneous tribe or village than when they undertake the formidable task of discovering the norms that exist in a complex modern nation-state composed of many disparate groups. The situation is further complicated by the nature of judgments about character, since such judgments are overly dependent on impressions and since, furthermore, impressions are usually stated in qualitative terms, it is impossible to make a reliable comparison between the national characters of two countries.

　　17. The authors main point in the passage is that national character

　　 is too elusive to merit attention by anthropologists and other social scientists

　　 is of greater interest to social scientists today than it has been in the past

　　 is still too difficult to describe with the precision required by many social scientists

　　 has become increasingly irrelevant because of the complexity of modern life

　　 can be described more accurately by anthropologists than by other social scientists

　　18. Given the information in the passage, which of the following is NOT true of modern nation-states?

　　 They are complex.

　　 They are heterogeneous.

　　 They are of interest to social scientists.

　　 They lack cultural norms.

　　 They differ from one another in terms of national character.

　　19. It can be inferred from the passage that the social scientists mentioned in lines 1-7 would agree with which of the following statements?

　　I. It is extremely difficult to create models that account for both economic and social development.

　　II. Models of economic and social development would be improved by the inclusion of adequate descriptions of national character.

　　III. It is important to supplement formal models of economic and social development with qualitative impressions of national character.

　　 I only

　　 II only

　　 III only

　　 I and III only

　　 II and III only

　　20. Which of the following best describes the organization of the passage?

　　 A problem is presented and reasons for its existence are supplied.

　　 A controversial view is presented and evidence for its validity is supplied.

　　 A hypothesis is presented and possible means of verifying it are suggested.

　　 A recent development is described and then analyzed.

　　 A dispute is summarized and one side defended.

　　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 精制食盐). The fundamental components of an ionic salt are ions: atoms or molecules that have become electrically charged by gaining or losing one or more electrons. In forming sodium chloride, for example, sodium atoms give up an electron and chlorine atoms gain an electron . 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 called an electride. In electrides, the anions are completely replaced by electrons, which are trapped in naturally formed cavities within a framework of regularly stacked cations . 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 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 depend 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 large 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 frame-work 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 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 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 batteries. One obstacle is the tendency of electrides to decompose through reaction with air and water. Researchers are seeking ways to increase their stability.

　　21. The passage is primarily concerned with discussing

　　 a way to isolate electrons

　　 the characteristics of a new kind of crystal

　　 the structure of an ionic salt

　　 commercial uses for electrides

　　 the properties of ions

　　22. In the first paragraph, the author is primarily concerned with

　　 introducing a variant on the standard atomic theory

　　 describing how chlorine atoms can become negatively charged

　　 describing some early research at Michigan State University

　　 presenting the identifying properties of an electride

　　 providing background for the technical discussion to follow

　　23. It can be inferred from the passage that the differences between the behavior of anionic electrons and normal anions result from which of the following features of electrons, as compared to normal anions?

　　I. The much lower mass of electrons

　　II. The much greater tendency of electrons to interact with one another over large distances

　　III. The much greater likelihood of electrons to remain trapped in naturally formed anionic cavities

　　 I only

　　 II only

　　 I and II only

　　 I and III only

　　 II and III only

　　24. According to the passage, the defining characteristic of an electride is which of the following?

　　 Its positive ions are of particularly low mass.

　　 Its ions possess identical electrical charges.

　　 It contains a framework of regularly stacked ions.

　　 Its ions demonstrate strong mutual attraction.

　　 Its negative ions consist solely of electrons.

　　25. It can be inferred from the passage that anions behaving as simple charged spheres could be expected to

　　 readily lose electrons and become positively charged

　　 move freely in and out of their cavities

　　 respond to photons by liberating electrons

　　 stack with other anions to create a regular framework

　　 remain fixed relative to their cations

　　26. It can be inferred from the passage that an electride behaves most like a normal ionic crystal when the electride has which of the following features?

　　 The anionic cavities are widely separated.

　　 All of the trapped electrons are able to delocalize.

　　 The trapped electrons are liberated by impinging photons.

　　 The ions are tightly packed together.

　　 Most of the cations have lost their electrical charge.

　　27. With which of the following statements regarding electrides would the author most likely agree?

　　 They have proven themselves to be of great commercial value.

　　 Their future commercial value is promising but uncertain.

　　 They are interesting but of no practical value.

　　 They have commercial value mainly in solar-energy applications.

　　 Their principal importance will lie in scientific research.

答案：17-27：CDBABECEEAB