问答题(1) When a molten metal or metallic alloy is cooled to a solid, a crystalline structure is formed that depends on the particular alloy composition. (2) In contrast, molten nonmetallic glass-forming materials, when cooled, do not assume a crystalline structure, but instead retain a structure somewhat like that of the liquid—an amorphous structure. (3) At room temperature, the natural long-term tendency for both types of materials is to assume the crystalline structure. (4) {{U}}The difference between the two is in the kinetics or rate of formation of the crystalline structure, which is controlled by factors such as the nature of the chemical bonding and the ease with which atoms move relative to each other.{{/U}} (5) Thus, in metals, the kinetics favors rapid formation of a crystalline structure, whereas in nonmetallic glasses the rate of formation is so slow that almost any cooling rate is sufficient to result in an amorphous structure. Select the sentence in which the author illustrates the causes of the rate of formation of the crystalline structure.

问答题It is well known that biological changes at the molecular level have morphogenetic consequences, consequences affecting the formation and differentiation of tissues and organs. It is superfluous to point out that gene mutations and disturbances of the biosynthetic processes in the embryo may result in abnormalities in the morphology (structure) of an organism. However, whereas much is known about causes and consequences at the molecular level, and in spite of an enormous accumulation of chemical and morphological data on embryos of various kinds, {{U}}our understanding of how genes control morphogenesis is still far from complete. Perhaps one reason for this is that molecular biologists and morphologists speak different languages.{{/U}} Whereas the former speak about messenger-RNA and conformational changes of protein molecules, the latter speak of ectoderms, hypoblasts, and neural crests. {{U}}One solution to this predicament is to try to find some phenomena relevant to morphogenesis which both the molecular biologist and the morphologist can understand and discuss.{{/U}} As morphogenesis must be basically the result of changes in behavior of the individual cells, it seems logical to ask morphologists to describe the morphogenetic events observed in terms of changes in cellular contact, changes in the rate of proliferation of cells, or similar phenomena. Once this is done, it may be appropriate to ask questions about the molecular background for these changes. One may, for instance, ask whether variations in cell contact reflect alterations in the populations of molecules at the cell surface, or one may inquire about the molecular basis for the increased cell mobility involved in cell dispersion. Studies of this kind have been carried out with cells released from tissues in various ways and then allowed to reveal their behavior after being spread out into a thin layer. In many cases, such cells show the ability to reaggregate, after which different cell types may sort themselves out into different layers and even take part in still more intricate morphogenetic events. But in most cases, the behavior of cells in the intact embryo is difficult to study because of the thickness and opacity of the cell masses. The sea urchin embryo, however, has the advantage that it is so transparent that each cell can be easily observed throughout development. Thus, {{U}}by recording the development of a sea urchin embryo with time-lapse photography, the research scientist might discover previously unknown features of cellular behavior. Perhaps the study of the sea urchin in this manner can provide a medium by which the molecular biologist and the morphologist can begin communicating with each other more effectively about the way in which genes control morphogenesis.{{/U}}

问答题{{U}}Bracken fern has been spreading from its woodland strongholds for centuries,{{/U}} but the rate of encroachment into open countryside has lately increased alarmingly throughout northern and western Britain. A tough competitor, bracken {{U}}reduces the value of grazing land{{/U}} by crowding out other vegetation. The fern is itself poisonous to livestock, and also encourages proliferation of sheep ticks, which {{U}}not only attack sheep but also transmit diseases{{/U}}. No less important to some people are bracken's effects on threatened habitats and on the use of uplands for recreational purposes, even though many appreciate its beauty. {{U}}Biological controls may be the only economic solution.{{/U}} One potentially cheap and self-sustaining method of halting the spread of bracken is to introduce natural enemies of the plant. Initially unrestrained by predators of their own, foreign predators are likely to be able to multiply rapidly and overwhelm intended targets. Because bracken occurs throughout the world, there is plenty of scope for this approach. Two candidates, both moths from the Southern Hemisphere, are now being studied. {{U}}Of course, biological control agents can safely be released only if it can be verified that they feed solely on the target weed. The screening tests have so far been fraught with difficulties.{{/U}} The first large shipment of moths succumbed to a disease. Growing enough bracken indoors is difficult, and the moths do not readily exploit cut stems. These are common problems with rearing insects for biological control. {{U}}Other problems can be foreseen. Policymakers need to consider many factors and opinions such as the cost of control compared to existing methods, and the impact of the clearance of bracken on the landscape, wildlife, and vegetation.{{/U}} In fact, scientists already have much of the information needed to assess the impact of biological control of bracken, but it is spread among many individuals, organizations, and government bodies. The potential gains for the environment are likely to outweigh the losses because few plants, insects, mammals, and birds live associated only with bracken, and many would benefit from a return of other vegetation or from a more diverse mosaic of habitats. But legal consequences of attempts at biological control present a potential minefield. For example, many rural tenants still have the right of "estoyers", the right to cut bracken as bedding for livestock and uses. What would happen if they were deprived of these rights? Once a biological control agent is released, it is difficult to control its speed. What consideration is due landowners who do not want to control bracken? According to law, the release of the biological control agents must be authorized by the secretary of state for the environment. But Britain lacks the legal and administrative machinery to assemble evidence for and against release.

问答题{{U}}A mysterious phenomenon is the ability of over-water migrants to travel on course.{{/U}} Birds, bees, and other species can keep track of time without any sensory cues from the outside world, and such "biological clocks" clearly contribute to their "{{U}}compass sense{{/U}}". For example, they can use the position of the Sun or stars, along with the time of day, to find north. But compass sense alone cannot explain how birds navigate the ocean: after a flock traveling east is blown far south by a storm, it will assume the proper northeasterly course to compensate. Perhaps, some scientists thought, migrants determine their geographic position on Earth by celestial navigation, almost as human navigators use stars and planets, but this would demand of the animals a fantastic map sense. Researchers now know that some species have a magnetic sense, which might allow migrants to determine their geographic location by detecting variations in the strength of the Earth's magnetic field.

问答题(1) Properly speaking, a movement is a continuous, collective effort to bring about fundamental social reform and it is a collaborative rather than an individualistic enterprise. (2) No matter how many factions are involved, there is always a common objective. (3) The Black freedom struggle of the 1960' was such an effort. (4) Its objective was to transform the manner in which Black Americans in the United States were viewed and treated. (5) And Black writers and artists sought to transform the manner in which Black Americans were represented or portrayed in literature and the arts. Select the sentence in the passage that defines the meaning of a term.

问答题 These exercises are designed to help you apply the mathematics concepts just covered. They are not in GRE format, but should help you to identify your areas of strength and weakness. Coordinate Geometry These questions will test your knowledge of operations involving the equation and the slope of a line and distance and midpoint formulas. Answer the following questions.

问答题如果证据表明当地居民即便喜欢爵士乐，也决定不去爵士俱乐部消费，那么作者关于爵士俱乐部能盈利的说法会被削弱。

问答题 These exercises are designed to help you apply the mathematics concepts just covered. They are not in GRE format, but should help you to identify your areas of strength and weakness. Linear Equations with One Variable These questions will test your knowledge of linear equations involving one variable. Solve the following equations.

问答题这些对立的观点建立在这样一个假说之上：环境保护和经济发展本质上是彼此排斥的(mutually exclusive)。

问答题即便北极鹿的数量的确下降了，但把这种下降归因于迁徙模式改变而造成的食物短缺是不能让人信服的。

问答题Issue Topic "A formal education is nothing more than the relentless revelation of one"s own ignorance." Discuss the extent to which you agree or disagree with the claim made above. Use relevant reasons and examples to support your point of view.

问答题尽管作者呼吁环境保护的动机可以理解，但他没能提出足够多的确凿证据来证明支持这位主张环保的候选人(pro-environmentalist candidate)的合理性。 *提示：用justify(证明……的合理性)。

问答题{{U}}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.{{/U}} {{U}}That view{{/U}}, based on 100 years of observations made around the globe, {{U}}produced only a rough approximation of the true circulation.{{/U}} But in the 1950's and the 1960's, {{U}}researchers began to employ newly developed techniques and equipment,{{/U}} 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. {{U}}These instruments disclosed an unexpected level of variability in the deep ocean.{{/U}} 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 of the major currents. Mesoscale phenomena—the oceanic analogue of weather systems—often 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). {{U}}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 occasional—but far-reaching—climatic events such as E1 Nino,{{/U}} the atmospheric-oceanic disturbance in the equatorial Pacific that affects global weather patterns. {{U}}Unfortunately, it is not feasible to use conventional techniques to measure mesoscale fields.{{/U}} To measure 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, {{U}}it was proposed in 1979 that tomography be adapted to measuring the physical properties of the ocean.{{/U}} In medical tomography x-rays map the human body's density variations (and hence internal organs); the information from the x-rays, transmitted through the body along many different paths, is recombined to form three-dimensional images of the body's interior. It is primarily this multiplicative increase in data obtained from the multipath transmission of signals that accounts for oceanographers' attraction to tomography: {{U}}it allows the measurement of vast areas with relatively few instruments.{{/U}} Researchers 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 ocean's interior—its temperature, 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.

问答题Task 2: Argument Analysis Directions: In 30 minutes, prepare a critical analysis of an argument expressed in a short paragraph. You may not offer an analysis of any other argument. Write your essay on the lined page that follows. As you critique the argument, think about the author's underlying assumptions. Ask yourself whether any of them are questionable. Also evaluate any evidence the author brings up. Ask yourself whether it actually supports the author's conclusion. In your analysis, you may suggest additional kinds of evidence to reinforce the author's argument. You may also suggest methods to refute the argument, or additional data that might be useful to you as you assess the soundness of the argument. You may not, however, present your personal views on the topic. Your job is to analyze the elements of an argument, not to support or contradict that argument. Faculty members from various institutions will judge your essay, assessing it on the basis of your skill in the following areas: · Identification and assessment of the argument's main elements · Organization and articulation of your thoughts · Use of relevant examples and arguments to support your case · Handling of the mechanics of standard written English Topic The following appeared in a petition presented by Classen University students to the school's administration. The purpose of higher education is to prepare students for the future, but Classen students are at a serious disadvantage in the competition for post-college employment due to the University's burden- some breadth requirements. Classen's job placement rate is substantially lower than placement rates of many top-ranked schools. Classen students would be more attractive to employers if they had more time to take advanced courses in their specialty, rather than being required to spend fifteen percent of their time at Classen taking courses outside of their subject area. We demand, therefore, that the University abandon or drastically cut back on its breadth requirements.

问答题Warm-blooded animals have elaborate physiological controls to maintain constant body temperature (in humans, 37℃). Why then during sickness should temperature rise, apparently increasing stress on the infected organism? It has long been known that the level of serum iron in animals falls during infection. Garibaldi first suggested a relationship between fever and iron. He found that microbial synthesis of siderophores—substances that bind iron—in bacteria of the genus Salmonella declined at environmental temperatures above 37℃ and stopped at 40.3℃. Thus, fever would make it more difficult for an infecting bacterium to acquire iron and thus to multiply. Cold-blooded animals were used to test this hypothesis because their body temperature can be controlled in the laboratory. Kluger reported that of iguanas infected with the potentially lethal bacterium A.hydrophilia, more survived at temperatures of 42℃ than at 37℃, even though healthy animals prefer the lower temperature. When animals at 42℃ were injected with an iron solution, however, mortality rates increased significantly. Research to determine whether similar phenomena occur in warm-blooded animals is sorely needed.

问答题{{U}}Hydrogeology is a science dealing with the properties, distribution, and circulation of water on the surface of the land, in the soil and underlying rocks, and in the atmosphere.{{/U}} The hydrologic cycle, a major topic in this science, is the complete cycle of phenomena through which water passes, beginning as atmospheric water vapor, passing into liquid and solid form as precipitation, thence along and into the ground surface, and finally again returning to the form of atmospheric water vapor by means of evaporation and transpiration. {{U}}The term "geohydrology" is sometimes erroneously used as a synonym for "hydrogeology".{{/U}} Geohydrology is concerned with underground water. There are many formations that contain water but are not part of the hydrologic cycle because of geologic changes that have isolated them underground. These systems are properly termed geohydrologic but not hydrogeologic. Only when a system possesses natural or artificial boundaries that associate the water within it with the hydrologic cycle may the entire system properly be termed hydrogeologic.

问答题接下来需要考虑的问题与学生对于荣誉守则(honor codes)的真实遵守程度有关，因为仅仅采访受到荣誉守则约束的学生不太可能得到其遵守情况的客观信息。

问答题 Polynomial Operations and Factoring Simple Quadratic Equations These questions will test your knowledge of operations involving polynomial operations and factoring simple quadratic equations. Solve the following equations.

问答题这个观点在本质上涉及了教育在人类社会中的作用的问题。

问答题 Exponents These questions will test your knowledge of operations using exponents. Fill in the blanks below with the correct number.