单选题In July 1994, the comet(彗星) Shoemaker-Levy 9 smashed into the planet Jupiter. For the first time, humans were able to witness exactly what happens when a celestial(天空的) body collides with a planet and it quickly became clear that survival was no longer entirely a question of being the "fittest". A new factor had been introduced into evolution: the ability to survive a collision between the earth and an asteroid (小行星) or comet. To most people, the risk remains academic. With all the dangers humans face -- sickness, accidents- it is understandable that people don't take seriously the risks posed by something that hasn't happened for 65 million years and may not happen for another 65 million years. However, many scientists believe that collisions between the earth and celestial bodies cannot be regarded as "just another risk". The main reason for this is that no other disaster -- except perhaps a nuclear war -- has the potential to destroy human civilization completely. Even the worst floods and earthquakes affect only a very small percentage of the earth's surface and population. But the effects of an impact caused by a celestial body of just ten kilometers in diameter would make humans extinct, along with most of the world's other animals and plants. The danger comes from asteroids and comets which cross the earth's orbit. Asteroids pose a greater danger because they are more numerous. Those less than 100 meters in diameter are not usually regarded as a threat bemuse most are destroyed by heat as they enter the earth's atmosphere and so never reach the ground. It is those asteroids with diameters of one kilometer or more which pose the greatest threat.

单选题Text 4 In the atmosphere, carbon dioxide acts rather like a one-way mirror—the glass in the roof of a greenhouse which allows the sun's rays to enter but prevents the heat from escaping. According to a weather expert's prediction, the atmosphere will be 3℃ warmer in the year 2050 than it is today, if man continues to burn fuels at the present rate. If this warming up took place, the ice caps in the poles would begin to melt, thus raising sea level several metes and severely flooding coastal cities. Also, the increase in atmospheric temperature would lead to great changes in the climate of the northern hemisphere, possibly resulting in an alteration of the earth's chief food-growing zones. In the past, concern about a man-made warming of the earth has concentrated on the Arctic because the Antarctic is much colder and has a much thicker ice sheet. But the weather experts are now paying more attention to West Antarctic, which may be affected by only a few degrees of warming: in other words, by a warming on the scale that will possibly take place in the next fifty years from the burning of fuels. Satellite pictures show that large areas of Antarctic ice are already disappearing. The evidence available suggests that a warming has taken place. This fits the theory that carbon dioxide warms the earth. However, most of the fuel is burnt in the northern hemisphere, where temperatures seem to be failing. Scientists conclude, therefore, that up to now natural influences on the weather have exceeded those caused by man. The question is: Which natural cause has most effect on the weather? One possibility is the variable behavior of the sun. Astronomers at one research station have studied the hot spots and "cold" spots (that is, the relatively less hot spots) on the sun. As the sun rotates, every 27.5 days, it presents hotter or "colder" faces to the earth, and different aspects to different parts of the earth. This seems to have a considerable effect on the distribution of the earth's atmospheric pressure, and consequently on wind circulation. The sun is also variable over a long term: its heat output goes up and down in cycles, the latest trend being downward. Scientists are now finding mutual relations between models of solar-weather interactions and the actual climate over many thousands of years, including the last Ice Age. The problem is that the models are predicting that the world should be entering a new Ice Age and it is not. One way of solving this theoretical difficulty is to assume a delay of thousands of years while the solar effects overcome the inertia of the earth's climate. If this is right, the warming effect of carbon dioxide might thus be serving as a useful counter-balance to the sun's diminishing heat.

单选题Children don't ______ understand what are reciting, but gradually it will have an impact on thinking. A. necessarily B. profitably C. unnecessarily D. unprofitably

单选题Cars account for half the oil consumed in the U.S. , about half the urban pollution and one fourth the greenhouse (温室) gases. They take a similar toll of (损耗) resources in other industrial nations and in the cities of the developing world. As vehicle use continues to increase in the coming decade, the U.S. and other countries will have to deal with these issues or else face unacceptable economic, health-related and political costs. It is unlikely that prices will remain at their current low level or that other nations will accept a large and growing U.S. contribution to global climatic change. Policymakers and industry have four options: reduce vehicle use, increase the efficiency and reduce the emissions of conventional gasoline-powered vehicles, switch to less harmful fuels, or find less polluting driving systems. The last of these—in particular the introduction of vehicles powered by electricity—is ultimately the only sustainable option. The other alternatives are attractive in theory but in practice are either impractical or offer only marginal improvements. For example, reduced vehicle use could solve traffic problems and a host of social and environmental problems, but evidence from around the world suggests that it is very difficult to make people give up their cars to any significant extent. In the U.S. , mass-transit ridership and carpooling (合伙用车) have declined since World War Ⅱ. Even in western Europe, with fuel prices averaging more than ＄1 a liter (about ＄4 a gallon) and with easily accessible mass transit and dense populations, cars still account for 80 percent of all passenger travel. Improved energy efficiency is also appealing, but automotive fuel economy has barely made any progress in 10 years. Alternative fuels such as natural gas, burned in internal-combustion engines, could be introduced at relatively low cost, but they would lead to only marginal reductions in pollution and greenhouse emissions (especially because oil companies are already spending billions of dollars every year to develop less polluting types of gasoline).

单选题We felt______ to death because we could make nothing of the lecturer's speech.

单选题The second book was ______ by August 1952, but two years later, the end was still nowhere in sight. A. completed B. to complete C. to have completed D. to have been completed

单选题For centuries, explorers have risked their lives venturing into the unknown for reasons that were to varying degrees economic and nationalistic. Columbus went west to look for better trade routes to the Orient and to promote the greater glory of Spain. Lewis and Clark journeyed into the American wilderness to find out what the U.S. had acquired when it purchased Louisiana, and the Apollo astronauts rocketed to the moon in a dramatic show off technological muscle during the cold war. Although their missions blended commercial and political-military imperatives, the explorers involved all accomplished some significant science simply by going where no scientists had gone before. Today Mars looms (隐约出现) as humanity's next great terra incognita (未探明之地). And with doubtful prospects for a short-term financial return, with the cold war a rapidly fading memory and amid a growing emphasis on international cooperation in large space ventures, it is clear that imperatives other than profits or nationalism will have to compel human beings to leave their tracks on the planet's reddish surface. Could it be that science, which has long played a minor role in exploration, is at last destined to take a leading role? The question naturally invites a couple of others: are there experiments that only humans could do on Mars? Could those experiments provide insights profound enough to justify the expense of sending people across interplanetary space? With Mars the scientific stakes are arguably higher than they have ever been. The issue of whether life ever existed on the planet, and whether it persists to this day, has been highlighted by mounting evidence that the Red Planet once had abundant stable, liquid water and by the continuing controversy over suggestions that bacterial fossils rode to Earth on a meteorite (陨石) from Mars. A more conclusive answer about life on Mars, past or present, would give researchers invaluable data about the range of conditions under which a planet can generate the complex chemistry that leads to life. If it could be established that life arose independently on Mars and Earth, the finding would provide the first concrete clues in one of the deepest mysteries in all of science: the prevalence of life in the universe.

单选题A: I'm going to pop out to get a sandwich. ______ B: No, thank you. I'm all right.

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单选题{{B}}练习二十{{/B}} What do the extraordinarily successful companies have in common? To find out, we looked for correlations. We know that correlations are not always reliable; nevertheless, in the 27 survivors, our group saw four shared personality traits that could explain their longevity. Conservatism in financing. The companies did not risk their capital gratuitously. They understood the meaning of money in an old-fashioned way; they knew the usefulness of spare cash in the kitty. Money in hand allowed them to snap up options when their competitors could not. They did not have to convince third-party financiers of the attractiveness of opportunities they wanted to pursue. Money in the kitty allowed them to govern their growth and evolution. Sensitivity to the world around them. Whether they had built their fortunes on knowledge (such as Dupont’s technological innovations) or on natural resources (such as the Hudson's Bay Company's access to the furs of Canadian forests), the living companies in our study were able to adapt themselves to changes in the world around them. As wars, depressions, technologies, and politics surged and ebbed, they always seemed to excel at keeping their feelers out, staying attuned to whatever was going on. For information, they sometimes relied on packets carried over vast distances by portage and ship, yet they managed to react in a timely fashion to whatever news they received. They were good at learning and adapting. Awareness of their identity. No matter how broadly diversified the companies were, their employees all felt like parts of a whole. Lord Cole, chairman of Unilever in the 1960s, for example, saw the company as a fleet of ships. Each ship was independent, but the whole fleet was greater than the sum of its parts. The feeling of belonging to an organization and identifying with its achievements is often dismissed as soft. But case histories repeatedly show that a sense of community is essential for long-term survival. Managers in the living companies we studied were chosen mostly from within, and all considered themselves to be stewards of a longstanding enterprise. Their top priority was keeping the institution at least as healthy as it had been when they took over. Tolerance of new ideas. The long-lived companies in our study tolerated activities in the margin: experiments and eccentricities that stretched their understanding. They recognized that new businesses may be entirely unrelated to existing businesses and that the act of starting a business need not be centrally controlled. W.R. Grace, from its very beginning, encouraged autonomous experimentation. The company was founded in 1854 by an Irish immigrant in Peru and traded in guano, a natural fertilizer, before it moved into sugar and tin. Eventually, the company established Pan American Airways. Today it is primarily a chemical company, although it is also the leading provider of kidney dialysis services in the United States. By definition, a company that survives for more than a century exists in a world it cannot hope to control. Multinational companies are similar to the long-surviving companies of our study in that way. The world of a multinational is very large and stretches across many cultures. That world is inherently less stable and more difficult to influence than a confined national habitat. Multinationals, like enduring companies, must be willing to change in order to succeed. These four traits form the essential character of companies that have functioned successfully for hundreds of years. Given this basic personality, what priorities do the managers of living companies set for themselves and their employees?

单选题You may borrow the book ______ you keep it clean. A. such as B. so as to C. so long as D. as for

单选题Passage 5 Some houses are designed to be smart. Others have smart designs. An example of the second type of house won an Award of Excellence from the American Institute of Architects. Located on the shore of Sullivan's Island off the coast of South Carolina, the award-winning cube-shaped beach house was built to replace one smashed to pieces by Hurricane Hugo 10 years ago. In September 1989, Hugo struck South Carolina, killing 18 people and damaging or destroying 36,000 homes in the state. Before Hugo, many new houses built along South Carolina's shoreline were poorly constructed, and enforcement of building codes wasn't strict, according to architect Ray Huff, who created the cleverly-designed beach house. In Hugo's wake, all new shoreline houses are required to meet stricter, better-enforced codes. The new beach house on Sullivan's Island should be able to withstand a Category 3 hurricane with peak winds of 179 to 209 kilometers per hour. At first sight, the house on Sullivan's Island looks anything but hurricane-poor. Its redwood shell makes it resemble "a large party lantern" at night, according to one observer. But looks can be deceiving. The house's wooden frame is reinforced with long steel rods to give it extra strength. To further protect the house from hurricane damage, Huff raised it 2.7 meters off the ground on timber pilings--long, slender columns of wood anchored deep in the sand. Pilings might appear insecure, but they are strong enough to support the weight of the house. They also elevate the house above storm surges. The pilings allow the surges to run under the house instead of running into it. "These swells of water come ashore at tremendous speeds and cause most of the damage done to beach-front buildings," said Huff. Huff designed the timber pilings to be partially concealed by the house's ground-to-roof shell. "The shell masks the pilings so that the house doesn't look like it's standing with its pant legs pulled up," said Huff. In the event of a storm surge, the shell should break apart and let the waves rush under the house, the architect explained.

单选题A spokesman said that the people had greatly ______ the pollution.

单选题He seemed immune ______ such emotions as jealousy, vanity, bitterness, anger and resentment.

单选题Directions: For each blank in the following passage, choose the best answer from the choices given below. Mark your answer on the ANSWER SHEET by drawing with a pencil a short bar across the corresponding letter in the brackets. The first and smallest unit that can be discussed in relation to language is the word. In speaking, the choice of words is {{U}} {{U}} 1 {{/U}} {{/U}}the utmost importance. Proper selection will eliminate one source of {{U}} {{U}} 2 {{/U}} {{/U}}breakdown in the communication cycle. Too often, careless use of words {{U}} {{U}} 3 {{/U}} {{/U}}a meeting of the minds of the speaker and listener. The words used by the speaker may {{U}} {{U}} 4 {{/U}} {{/U}}unfavorable reactions in the listener {{U}} {{U}} 5 {{/U}} {{/U}}interfere with his cornprehension; hence, the transmission-reception system breaks down. {{U}} {{U}} 6 {{/U}} {{/U}}, inaccurate or indefinite words may make {{U}} {{U}} 7 {{/U}} {{/U}}difficult for the listener to understand the {{U}} {{U}} 8 {{/U}} {{/U}}which is being transmitted to him. The speaker who does not have specific words in his working vocabulary may be {{U}} {{U}} 9 {{/U}} {{/U}}to explain or describe in a {{U}} {{U}} 10 {{/U}} {{/U}}that can be understood by his listeners.

单选题Any salesperson who sells more than the weekly ______ will receive a bonus. A. ratio B. quota C. allocation D. portion

单选题 Thirty-one million Americans are over 60 years of age, and twenty-nine million of them arehealthy, busy, productive citizens. By the year 2030, one in every five people in the UnitedStates will be over 60. Elderly people are members of the fastest-growing minority in this country.Many call this the "graying of America" In 1973, a group called the "Gray Panthers" was organized. This group is made up of youngand old citizens. They are trying to deal with the special problems of growing old in America. TheGray Panthers know that many elderly people have health problems; some cannot walk well,others cannot see or hear well. Some have financial problems; prices are going up so fast that theelderly can't afford the food, clothing, and housing they need. Some old people are afraid andhave safety problems. Others have emotional problems. Many elderly are lonely because of thedeath of a husband or a wife. The Gray Panthers know another fact, too. Elderly people want to beas independent as possible. So, the Gray Panthers are looking for ways to solve the specialproblems of the elderly. The president of the Gray Panthers is Maggie Kuhn, an active woman in her late 70s. Shetravels across the United States, educating both young and old about the concerns of elders. One ofthe problems she talks about is where and how elders live. She says that Americans do notencourage elders to live with younger people. As far as Maggie Kuhn is concerned, only elderswho need constant medical care should be in nursing homes. Maggie Kuhn knows that elders need education, too. She spends lots of time talking to groupsof older Americans. She encourages them to continue to live in their own houses if it is possible.She also tells them that it is important to live with younger people and to have children aroundthem. This helps elders to stay young at heart.

单选题James: Phil has decided to quit smoking. Kim: Again? ______ A. It's a difficult decision to make. B. Cigarettes-addiction is dangerous. C. He's a cigarette addict. D. I wonder how long it will last this time.

单选题Edison tested more than one thousand materials to see if they could _____ electric current and glow.