单选题

单选题Everyone has suffered from headaches, but 21 recently medical researchers were not certain what caused them. Blew research is giving us more 22 about two common types of headaches: tension headaches and migraine headaches. The most painful 23 are migraines, which 24 about eight to ten percent of the time and are 25 as a very sharp, throbbing pain. Most headaches, 26 , are tension headaches. They are unpleasant, of course, but not as painful as the migraine 27 . Usually they are experienced as a 28 ache on both sides of the head or in the back or forehead. These headaches are caused by the tightening of the muscles of the head and neck, which 29 causes the blood vessels to narrow, making it difficult for the brain to receive the oxygen (water, nutrition, blood) it needs. This is what causes the pain. Migraines, 30 , result from the blood vessels in the brain enlarging, causing swelling in the brain. This swelling results in terrible pain. The headache may last for a day or two and 31 the individual sick and weak. Migraines are apparently 32 , because several individuals in the same family usually have them. Doctors believe that the brains of these individuals 33 in unusual ways to small problems, like failing a test or eating unwisely. 34 there are warning. 35 before a migraine occurs, such as spots appearing before the eyes or a sick feeling in the 36 . If the person takes medicine or caffeine as soon as he or she begins to feel the headache coming 37 , it can be 38 Caffeine and the medicine, called ergot, cause the blood vessels to narrow. Once the headache 39 , sleep and a cool 40 on the head may help.

单选题 The devastating effects of earthquakes on human lives and property have encouraged the search for earthquake prediction. This challenge remains and contemporary seismologists continue to seek reliable methods for pinpointing the time, place and magnitude of individual quakes. One prediction technique involves an analysis of the recurrence rates of earthquakes as indicators of future seismic activity. Earthquakes are concentrated in certain areas of the world where tectonic plates such as the Pacific Plate, the Eurasian Plate and the African Plate meet and create fault zones and it is in these areas that seismologists focus their investigations. The tectonic plate model provides another tool for earthquake prediction by calculating the accumulated strain at plate boundaries. When the strain reaches a certain magnitude the pressure must be released and it is therefore hypothesized that in such eases an earthquake is imminent. The search for premonitory phenomena has received particular attention. In contrast to the ancient Greeks and Romans, who relied on the howling of dogs as a warning sign, modern seismologists have focused on physical evidence for an impending earthquake. Evidence of plate strain can be found by measuring relative movements in geodetic stations, while chemical changes also offer signals for seismologists. Using chemical-detection techniques, scientists established a link between the rise in the concentration of radon gas in mineral water and the subsequent earthquake. Analysis of the changes in magnetic properties and conductivity of rocks provides further data for prediction. The electrical and magnetic properties of crustal rocks particularly sensitive to strain and studies measuring changes which occur in these properties have provided promising results. The conductivity of crustal rock is determined by the degree to which the rock is saturated with fluid and the electrolytic properties of those fluids. Before large earthquakes, small fractures develop in rocks, which change the quantity of fluid present. These changes can be measured and provide useful predictive data. However, similar changes in the fluid-bearing capacity of rock can occur as a result of other factors such as changes in the water table, and therefore this technique is not entirely reliable. The belief that the behavior of birds, eats and dogs provides evidence of imminent earthquakes has recently gained credence. It is hypothesized that the animals are sensitive to the seismic waves which precede major quakes. In zones where earthquakes are known to occur, improved construction techniques can significantly reduce the effects of seismic waves. If more accurate information regarding the time and magnitude were available, governments could take even more effective measures to reduce the impact on human life. If an entirely accurate prediction technique became available, there would be significant social and political implications. An earthquake prediction in a major urban area would require governments to provide an effective evacuation strategy, necessitating massive resource and political will.

单选题{{B}}Passage Six{{/B}} Scientists have known for more than two decades that cancer is a disease of the genes. Something scrambles the DNA inside a nucleus, and suddenly, instead of dividing in a measured fashion, a cell begins to copy itself furiously. Unlike an ordinary cell, it never, stops. But describing the process isn't the same as figuring it out. Cancer cells are so radically different from normal ones that it's almost impossible to untangle the sequence of events that made them that way. So for years researchers have been attacking the problem by taking normal cells and trying to determine what changes will turn them cancerous - always Without success. According to a report in the current issue of Nature, a team of scientists based at M. I .T.'s Whitehead Institute for Biomedical Research has finally managed to make human ceils malignant -a feat they accomplished with two different cell types by inserting just three altered genes into their DNA. While these manipulations were done only in lab dishes and won't lead to any immediate treatment, they appear to be a crucial step in understanding the disease. This is a "landmark paper," wrote Jonathan Weitzman and Moshe Yaniv of the Pasteur Institute in Paris, in an accompanying commentary. The dramatic new result traces back to a breakthrough in 1983, when the Whitehead's Robert Weinberg and colleagues showed that mouse cells would become cancerous when subjected to two altered genes. But when they tried such alterations on human cells, they didn't work. Since then, scientists have learned that mouse cells differ from human cells in an important respect: they have higher levels of an enzyme called telomerase. That enzyme keeps caplike structures called telomeres on the ends of chromosomes from getting shorter with each round of cell division. Such shortening is part of a cell's aging process, and since cancer cells keep dividing forever, the Whitehead group reasoned that making human cells more mouselike might also make them cancerous. The strategy worked. The scientists took connective-tissue and kidney cells and introduce three altered genes—one that makes cells divide rapidly; another that disables two substances meant to rein in excessive division; and a third that promotes the production of telomerase, which made the cells essentially immortal. They'd created a tumor in a test tube. "Some people believed that telomerase wasn't that important," says the Whitehead's William Hahn, the study's lead author. "This allows us to say with some certainty that it is."

单选题Passage 4 To us it seems so natural to put up an umbrella to keep the water off when it rains. But actually the umbrella was not invented as protection against rain. Its first use was as a shade against the sun. Nobody knows who first invented it, but the umbrella was used in very ancient times. Probably the first to use it were the Chinese, was back in the eleventh century B. C. We know that the umbrella was used in ancient Egypt and Babylon as a sunshade. And there was a strange thing connected with its use: it became a symbol of honor and authority. In the Far East in ancient times, the umbrella was allowed to be used only by royalty or by those in high offices. In Europe, the Greeks were the first to use the umbrella as a sunshade. And the umbrella was in common use in ancient Greece. But it is believed that the first persons in Europe to use the umbrella as protection against rain were the ancient Romans. During the Middle Ages, the use of the umbrella practically disappeared. Then it appeared again in Italy in the late sixteenth century. And against it was considered a symbol of power and authority. By 1680, the umbrella appeared in France and later on in England. By the eighteenth century, the umbrella was used against rain throughout most of Europe. Umbrellas have not changed much in style during all this time, though they have become much lighter in weight. It wasn't until the twentieth century that women's umbrellas began to be made in a whole variety of colors.

单选题What occurred as told at the beginning of the passage?

单选题On his wanderings he"s ______ Spanish, Italian, French and a smattering of Russian.

单选题 Not too many decades ago it seemed "obvious" both to the general public and to sociologists that modern society has changed people's natural relations, loosened their responsibilities to kin (亲戚) and neighbors, and substituted in their place superficial relati onships with passing acquaintances. However, in recent years a growing body of research has revealed that the "obviousness" is not true. It seems that if you are city resident, you typically know a smaller proportion of your neighbors than you do if you are a resident of a smaller community. But, for the most part, this fact has few significant consequences. It does not necessarily follow that if you know few of your neighbors you will know no one else. Even in very large cities, people maintain close social ties within small, private social worlds. Indeed, the number and quality of meaningful relationships do not differ between more and less urban people Small-town residents are more involved with kin than are big-city residents. Yet city dwellers compensate by developing friendships with people who share similar interests and activities. Urbanism may produce a different style of life, but the quality of life does not differ between town and city. Nor are residents of large communities any likelier to display psychological symptoms of stress or alienation, a feeling of not belonging, than are residents of smaller communities. However, city dwellers do worry more about crime, and this leads them to a distrust of strangers. These findings do not imply that urbanism makes little or no difference. If neighbors are strangers to one another, they are less likely to sweep the sidewalk of an elderly couple living next door or keep an eye out for young troublemakers. Moreover, as Wirth suggested, there may be a link between a community's population size and its social heterogeneity (多样性). For instance, sociologists have found much evidence that the size of a community is associated with bad behavior including gambling, drugs, etc. Large-city urbanites are also more likely than their small-town counterparts to have a cosmopolitan (见多识广者的) outlook, to display less responsibility to traditional kinship roles, to vote for leftist political candidates, and to be tolerant of nontraditional religious groups, unpopular political groups, and so-called un-desirables. Everything considered, heterogeneity and unusual behavior seem to be outcomes of large population size.

单选题In fact, no matter what lengths others go to in their attempts to destroy your arguments or ______your confidence, you are certain to remain unmoved and unimpressed. A. erode B. undermine C. deprive D. underestimate

单选题The Timber rattlesnake is now on the endangered species list, and is extinct in two eastern states in which it once ______. A. thrived B. swelled C. prospered D. flourished

单选题Some biologists argue that each specifically human trait must have arisen gradually and erratically, and that it is therefore difficult to isolate definite ______ in the evolution of species.

单选题The method in which the writer believes is most effective for the poor benefiting from the rich is ______ .

单选题Unlike a judge, who must act alone, a jury discusses a case and then reaches its decision as a group, thus minimizing the effect of ______ bias.

单选题Our lives are woven together. As much as I enjoy my own【C1】______, I no longer imagine I can get through a single day completely【C2】______my own. Even if I am on【C3】______in the mountains, I am eating food someone else has grown, living in a house someone else has built, using electricity someone else is【C4】______to my house. Evidence of【C5】______is everywhere. As I was growing up, I remember【C6】______carefully taught that independence not interdependence was【C7】______. When I was face-to-face with【C8】______of some action, my mother's favorite remark was "【C9】______you've made your bed, lie on it. " Total independence is a dominant thing in our culture. I imagine【C10】______my parents were trying to teach me was to take responsibilities【C11】______my actions and my choices. And I grew up【C12】______that I was supposed to be totally independent and consequently became very【C13】______to ask for help. I would do almost anything not to be a【C14】______, and not require any help from anybody. When I became ill my illusions of total independence【C15】______in an instant. All of a【C16】______I had to face the fact that I could do nothing, not even sit up, 【C17】______someone else's intervention. I began to realize that not asking for help is, in fact, 【C18】______. I love to help people. If I don't let them help me back, I am not allowing them the【C19】______satisfaction I enjoy. Learning this lesson has allowed me once and for all to see that my life really is a part of a larger【C20】______.

单选题There are no solitary, free-living creature; every form of life is ______ other form.

单选题The reader can conclude that the Parthenon ______.

单选题The Untied States and Canada are lands of ______ except for the Indians, who are the only true natives.

单选题The headlights of the approaching car were so ______ that the cyclist had to stop riding. A.gleaning B.staring C.gleaming D.dazzling