单选题It is highly unlikely that she will arrive today.

单选题Mary looked pale and weary .

单选题{{B}}第三篇{{/B}} {{B}}Egypt Felled by Famine{{/B}} Even ancient Egypt's mighty pyramid builders were powerless in the face of the famine that helped bring down their civilisation around 2180 BC. Now evidence gleaned from mud deposited by the River Nile suggests that a shift in climate thousands of kilometres to the south was ultimately to blame--and the same or worse could happen today. The ancient Egyptians depended on the Nile's annual floods to irrigate their crops. But any change in climate that pushed the African monsoons southwards out of Ethiopia would have diminished these floods. Dwindling rains in the Ethiopian highlands would have meant fewer plants to stablise the soil. When rain did fall it would have washed large mounts of soil into the Blue Nile and into Egypt, along with sediment from the White Nile. The Blue Nile mud has a different isotope signature from that of the White Nile. So by analysing isotope differences in mud deposited in the Nile Delta, Michael Krom of Leeds University worked out what proportion of sediment came from each branch of the fiver. Krom reasons that during periods of drought, the amount of the Blue Nile mud in the river would be relatively high. He found that one of these periods, from 4,50Oto 4,200 years ago, immediately predates the fall of the Egypt's Old Kingdom. The weakened waters would have been catastrophic for the Egyptians. "Changes that affect food supply don't have to be very large to have a ripple effect in societies," says Bill Ryan of the Lamont Doherty Earth Observatory in New York. "Similar events today could be even more devastating," says team member Daniel Stanley, a geoarchaeologist from the Smithsonian Institutions in Washington, D. C.. "Anything humans do to shift the climate belts would have an even worse effect along the Nile system today because the populations have increased dramatically."

单选题The whale will be fed if he doesn't Uhunt/U for himself.

单选题{{B}}第二篇{{/B}} {{B}} Where Have All the Frogs Gone?{{/B}} In the 1980s, scientists around the world began to notice something strange: Frogs were disappearing. More recent research has shown that many kinds of amphibians (两栖动物) are declining or have become extinct. They have been around for a long time - over 350 million years. Why are they dying out now? Scientists are seriously concerned about this question. First of all, amphibians are an important source of scientific and medical knowledge. By studying amphibians, scientists have learned about new substances that could be very useful for treating human diseases. Further research could lead to many more discoveries, but that will be impossible if the amphibians disappear. The most serious aspect of amphibian loss, however, goes beyond the amphibians themselves. Scientists are beginning to think about what amphibian decline means for the planet as a whole. If the earth is becoming unlivable for amphibians, is it also becoming unlivable for other kinds of animals and human, beings as well? Scientists now believe that amphibian decline is due to several environmental factors. One of these factors is the destruction of habitat, the natural area where an animal lives. Amphibians are very sensitive to changes in their habitat. If they cannot find the right conditions, they will not lay their eggs. These days, as wild areas are covered with houses, roads, farms, or factories, many kinds of amphibians are no longer laying eggs. For example, the arroyo toad (蟾蜍) of southern California will only lay its eggs on the sandy bottom of a slow-moving stream. There are very few streams left in southern California, and those streams are often muddy because of building projects. Not surprisingly, the arroyo toad is now in danger of extinction. There are a number of other factors in amphibian decline. Pollution is one of them. In many industrial areas, air pollution has poisoned the rain, which then falls on ponds and kills the frogs and toads that live there. In farming areas, the heavy use of chemicals on crops has also killed off amphibians. Another factor is that air pollution has led to increased levels of ultraviolet (UV) light. This endangers amphibians, which seem to be especially sensitive to UV light. And finally, scientists have discovered a new disease that seems to be killing many species of amphibians in different parts of the world. All these reasons for the disappearance of amphibians are also good reasons for more general concern. The destruction of land, the pollution of the air and the water, the changes in our atmosphere, the spread of diseases - these factors affect human beings, too. Amphibians are especially sensitive to environmental change. Perhaps they are like the canary (金丝雀) bird that coal miners once used to take down into the mines to detect poisonous gases. When the canary became iii or died, the miners knew that dangerous gases were near and their own lives were in danger.

单选题 Can Buildings Be Designed to Resist Terrorist Attack In the aftermath of the terrorist attack on the World Trade Center, structural engineers are trying hard to solve a question that a month ago would have been completely unthinkable. Can building be designed to withstand catastrophic blasts inflicted by terrorists? Ten days after the terrorist attacks on the twin towers, structural engineers from the University at Buffalo and the Multidisciplinary Center for Earthquake Engineering Research (MCEER) headquartered at UB traveled to ground zero as part of a project funded by the National Science Foundation. Visiting the site as part of an MCEER reconnaissance visit, they spent two days beginning the task of formulating ideas about how to design such structures and searching for clues on how to do so in buildings that were damaged, but still are standing. "Our objective in visiting ground zero was to go and look at the buildings surrounding the World Trade Center, those buildings that are still standing, but that sustained damage," said M. Bruneau, Ph.D. " Our immediate hope is that we can develop a better understanding as to why those buildings remain standing, while our long-term goal is to see whether earthquake engineering technologies can be married to existing technologies to achieve enhanced performance of Buildings in the event of terrorist attacks." he added. Photographs taken by the investigators demonstrate in startling detail the monumental damage inflicted on the World Trade Center towers and buildings in the vicinity. One building a block away from the towers remains standing, but was badly damaged. "This building is many meters away from the World Trade Center and yet we see a column there that used to be part of that building", explained A. Whittaker, Ph. D. "The column became a missile that shot across the road, through the window and through the floor." The visit to the area also revealed some surprises, according to the engineers. For example, the floor framing systems in one of the adjacent buildings was quite rugged, allowing floors that were pierced by tons of falling debris to remain intact. "Highly redundant ductile framing systems may provide a simple, but robust strategy for blast resistance." he added. Other strategies may include providing alternate paths for gravity loads in the event that a load-bearing column fails." We also need a better understanding of the mechanism of collapse" , said A. Whittaker. "We need to find out what causes a building to collapse and how you can predict it." A. Reinhorn, Ph.D. noted that "earthquake shaking has led to the collapse of many buildings in the past. It induces dynamic response and extremely high stresses and deformations in structural components. Solutions developed for earthquake-resistant design may be directly applicable to blast engineering and terrorist-resistant design. Part of our mission now at UB is to transfer these solutions and to develop new ones where none exist at present."

单选题The sensation of a "lump in one's throat" arises from an increased flow of blood into the tissues of the pharynx and larynx. A. explanation B. disease C. feeling D. unpleasantness

单选题The little girl grasped her mother"s hand as she crossed the street.

单选题Messalina"s name has become a byword for notorious behavior.

单选题The room is dim and quiet.

单选题Global Warming At the Kyoto conference on global warming in December 1997, it became abundantly clear how complex it has become to work out international agreements relating to the environment because of economic concerns unique to each country. It is no longer enough to try to forbid certain activities or to reduce emissions of certain substances. The global challenges of the interlink between the environment and development increasingly bring us to the core of the economic life of states. During the late 1980s we were able, through international agreements, to make deep cuts in emissions harmful to the ozone layer. These reductions were made possible because substitutions had been found for many of the harmful chemicals and, more important, because the harmful substances could be replaced without negative effects on employment and the economies of states. Although the threat of global warming has been known to the world for decades and all countries and leaders agree that we need to deal with the problem, we also know that the effects of measures, especially harsh measures taken in some countries, would be nullified (抵消) if other countries do not control their emissions. Whereas the UN team on climate change has found that the emissions of carbon dioxide would have to be cut globally by 60% to stabilize the content of CO2 in the atmosphere, this path is not feasible for several reasons. Such deep cuts would cause a breakdown of the world economy. Important and populous (人口众多的) low or medium income countries are not yet willing to undertake legal commitments about their energy uses. In addition, the state of world technology would not yet permit us to make such a big leap. We must, however, find a solution to the threat of global warming early in the 21st century. Such a commitment would require a degree of shared vision and common responsibilities new to humanity. Success lies in the force of imaginations, in imagining what would happen if we fail to act. Although many living in cold regions would welcome the global warming effect of a warmer summer, few would cheer the arrival of the subsequent diseases, especially where there had been none.

单选题She had a natural courtesy combined with unshakable conviction .

单选题It is {{U}}postulated{{/U}} that a cure for the disease will have been found by the year 2020. A.challenged B.assumed C.deducted D.decreed

单选题I am not certain whether he will come.

单选题We can no longer put up with his actions.

单选题There is an abundant supply of cheap labor in this country. A. steady B. plentiful C. an extra D. a stable

单选题The express train went through the station with Ua mighty/U roar.

单选题 Irradiating Food Irradiating fruits, vegetables, pork and chicken to kill insects and bacteria has been approved by the Food and Drug Administration over the past decade or so. Irradiation of other meats, such as beef and lamb, is being reviewed. Federal approval does not require that industry adopt the process, and few food processors presently offer irradiated products. Market studies have shown that many consumers are afraid that eating irradiated foods may cause cancer, despite scientific studies that prove the safety of treated foods. Some people argue that more severe government inspection, higher food-safety standards, and more careful-preparation practices by consumers are all that is needed to ensure that food is safe. Consequently, companies currently see no need to spend millions of dollars outfitting processing plants with the equipment necessary for a process that very few shoppers are in favor of. All supermarkets that sell irradiated food must label the food either directly on the packaging, or, in the case of bulk items like fruits and vegetables, by placing a sign nearby. There is no requirement for the labeling of irradiated food served by chain restaurants or hospitals that buy directly from distributors, nor any regulations for products that contain irradiated ingredients. Presently, the FDA allows food to be treated with three types of radiation—gamma rays, high-energy electrons, and X rays—and sets limits on doses, depending on the type of food. The principle is that the dose to be used for a certain type of food should not exceed the amount that is sufficient to kill most harmful insects and bacteria present in it. Different types of food, because of their molecular compositions, may require different doses of radiation.

单选题The parents always restrain their daughter from swimming in the nearby pool.

单选题The audience at the music hall applauded enthusiastically after the piano solo. A. laughed B. clapped C. jumped D. chatted