单选题Valvular heart diseases are quite common, essentially resulting in impaired blood flow and were very difficult to treat. Some 30 years ago, it became possible to replace .diseased valves with prostheses to impose a greater control over blood flow. Early devices were of the mechanical variety, in which devices like ball-in-a-cage or tilting disc would be used to allow blood to flow under near-normal conditions. Although a few mechanical problems were encountered in the early days, the major difficulty lay with the tendency for any foreign material to initiate a blood clot. So, all valve recipients have to be given anticoagulant therapy. This is not particularly desirable for the patients, who may develop bleeding problems, and in any case is not always successful. Although good results are achieved with these valves, it was considered necessary to develop alternatives and the direction was that of natural tissues. It's not possible to transplant heart valves untreated because of rejection phenomena, but it became apparent that collagenous tissue could be cross-linked by glutaraldehyde and prepared in the form of a heart valve. Two sources of tissue were considered for this purpose, bovine pericardium ( collagenous tissue derived from the wall of a cow's heart) and porcine valves (heart valves taken from pigs) and the resulting "bioprosthetic valve" appeared to be very promising. It was particularly important that these patients didn't need anticoagulation. Unfortunately, these valves have not proved very durable, the cross-linked collagen suffering from slow calcification and deterioration so most of the replacement valves themselves need to be replaced within a decade. This would tend to suggest that the mechanical valves give superior performance, notwithstanding the anticoagulation problem, and a move back towards their use might have been expected. However, most of the valves in current use incorporate an alloy'( usually Stellite) for the housing, and a carbon coated occuluder. The complex shapes of some of the housing have required combinations of casting and welding technologies to be used in their construction and serious problems have arisen with a valve design from one manufacturer, where a small number of catastrophic fractures have occurred within the housing. In patients where this valve has been used to treat aortic valve disease, this fracture is usually fatal and although the risks are small, the problem is important to the industry. Also, at a time when this dichotomy is exercising the minds of surgeons, scientists and regulatory bodies alike, the emergence of the disease BSE in cattle has placed even further restrictions on the use of animal tissue for this type of application and the whole question of prosthetic heart valves has been turned from a reasonable successful example of reconstructive implant surgery to a very confused area. This serves to highlight some of the very varied problems of facing the use of biomaterials.

单选题He is ______ about his chances of winning a gold medal in the Olympics next year. [A] optimistic [B] optional [C] outstanding [D] obvious

单选题I have to say this, but this coat you've just bought is made of______ fur; it's not real mink.(2006年清华大学考博试题)

单选题Jane tried to______ at the swinging rope, but failed.

单选题On turning round the comer we saw the road______ steeply.

单选题The Americans and the British not only speak the same language but also a large number of social customs.

单选题 The Aleuts, residing on several islands of the Aleutian Chain, the Pribilof Islands, and the Alaskan peninsula have possessed a written language since 1825, when the Russian missionary Ivan Venation selected appropriate characters of the Cyrillic alphabet to represent Aleut speech sounds, recorded the main body of Aleut vocabulary and formulated grammatical rules. The Czarist Russian conquest of the proud, independent sea hunters was so devastatingly thorough that tribal traditions, even tribal memories, were almost obliterated. The slaughter of the majority of an adult generation was sufficient to destroy the continuity of tribal knowledge, which was dependent upon oral transmission. As a consequence, the Aleuts developed a fanatical devotion to their language as their only cultural heritage. The Russian occupation placed a heavy linguistic burden on the Aleuts. Not only were they compelled to learn Russian to converse with their overseers and governors, but they had to learn Old Slavonic to take an active part in church services as well as to master the skill of reading and writing their own tongue. In 1867, when the United States purchased Alaska, the Aleuts were unable to break sharply with their immediate past and substitute English for any one of their three languages. To communicants of the Russian Orthodox Church a knowledge of Slavonic remained vital as did Russian, the language in which one conversed with the clergy. The Aleuts came to regard English education as a device to wean them from their religious faith. The introduction of compulsory English schooling caused a minor renascence of Russian culture as the Aleut parents sought to counteract the influence of the schoolroom. The harsh life of the Russian colonial rule began to appear more happy and beautiful in retrospect. Regulations forbidding instruction in any language other than English increased its unpopularity. The superficial alphabetical resemblance of Russian and Aleut linked the two tongues so closely that every restriction against teaching Russian was interpreted as an attempt to eradicate the Aleut tongue. From the wording of many regulations, it appears that American administrators often had not the slightest idea that the Aleuts were clandestinely reading and writing their own tongue or even had a written language of their own. To too many officials, anything in Cyrillic letters was Russian and something to be stamped out. Bitterness bred by abuses and the exploitations the Aleuts suffered from predatory American traders and adventurers kept alive the Aleut resentment against the language spoken by Americans. Gradually despite the failure to emancipate the Aleuts from a sterile past by relating the Aleut and English languages more closely, the passage of years has assuaged the bitter misunderstandings and caused an orientation, away from Russian toward English as their second language, but Aleut continues to be the language that molds their thought and expression.

单选题Tests conducted at the University of Pennsylvania's Psychological Laboratory showed that anger is one of the most difficult emotions to detect from facial expression. Professor Dallas E. Buzby confronted 716 students with pictures of extremely angry persons, and asked them to identify the emotion from facial expression. Only 2 percent made correct judgments. Anger was most frequently judged as "pleased." And a typical reaction of a student with the picture of a man who was hopping mad was to classify his expression as either "bewildered", "quizzical", or simply "amazed". Other students showed that it is extremely difficult to tell whether a man is angry or not just by looking at his face. The investigators found further that women are better at detecting anger from facial expression than men are. Paradoxically, they found that psychological training does not sharpen one's ability to judge a man's emotions by his expressions but appears actually to hinder it. For in the university tests, the more courses the subjects had taken in psychology, the poorer judgment scores he turned in.

单选题The economic situation (will improve) given that there is (forecast to be) less unemployment and (closures) than (in previous years).

单选题The couple had been trying to satisfy all the needs of their only youngster, who had been______ for more pocket money all the time.(2006年厦门大学考博试题)

单选题I don't mind a bit if you bring your friends in for a drink, but it is rather too much when ten people arrive ______for dinner.

单选题 Passage 4 One reaction to all the concern about tropical deforestation is a blank stare that asks the question, "Since I don't live in the tropics, what does it have to do with me?" The answer is that your way of life, wherever you live in the world, is tied to the tropics in many ways. If you live in a house, wash your hair, eat fruit and vegetables, drink soda, or drive a car, you can be certain that you are affected by the loss of tropical' forests. Biologically, we are losing the richest regions on earth when, each minute, a piece of tropical forest the size of ten city blocks vanishes. As many as five million species of plants, animals and insects, 40 to 50 percent of all living things, live there, and are being irrevocably lost faster than they can be found and described. Their loss is incalculable. Take medicine, for example. Less than one percent of tropical forest plants have been examined for their chemical compounds. Nonetheless, scientists have integrated a wealth of important plants into our everyday lives. The West African calabar bean is used to treat glaucoma, while the sankerfoot plant of India yields reserpine, essential for treating hypertension. A West African vine provides the basis for strophanthus, a heart medicine. Quinine, an alkaloid derived from boiling the bark of the cinchona tree, is used to prevent and treat malaria. Derivatives from the rosy periwinkle offer a 99 percent chance of remission for victims of lymphocytic leukemia, as well as a 59 percent chance of recovery from Hodgkin's disease. In fact, of the 3, 000 plant species in the world known to contain anti-cancer properties, 2, 100 are from the tropical rain forest. Then there is rubber. For many uses, only natural rubber from trees will do, synthetics are not good enough. Today, over half of the world's commercial rubber is produced in Malaysia and Indonesia, while the Amazon's rubber industry produces much of the world's four million tons. Adding ammonia to rubber produces latex which is used for surgical gloves, balloons, adhesives, and foam rubber. Latex, plus a weak mixture of acid results in sheet rubber used for footwear and many sporting goods. Literally thousands of tropical plants are valuable for their industrial uses. Many provide fiber and canes for furniture, soundproofing and insulation. Palm oil, a product of the tropics, brings to your table margarine, cooking oil, bakery products, and candles. Palm nut oil, from the seed kernel inside the fruit, is found in soap, candles, and mayonnaise. The sap from Amazonian copaiba trees, poured straight into a fuel tank, can power a truck. At present, 20 percent of Brazil's diesel fuel comes from this tree. An expanded use of this might reduce our dependency on irreplaceable fossil fuels. Many scientists assert that deforestation contributes to the greenhouse effect, the heating of the earth from increased carbon dioxide in the atmosphere. As we destroy forests, we lose their ability to convert carbon dioxide into oxygen. Carbon dioxide levels could double within the next half-century, warming the earth by as much as 4. 5 degrees. The result? A partial meltdown of the polar ice caps, raising sea levels as much as 24 feet. A rise of 15 feet would threaten anyone living within 35 miles of the coast. Far-fetched? Perhaps, but scientists warn that by the time we realize the severe effects of tropical deforestation, it will be 20 years too late. Can tropical deforestation affect our everyday lives? We only have to look at the catalogued tropical forests and the abundance of wondrous products from which we benefit every day to know the answer. After all, the next discovery could be a cure for cancer or the common cold, or the answer to feeding the hungry, or fuelling our world for centuries to come.Comprehension Questions

单选题Real Policemen hardly recognize any resemblance between their lives and what they see on TV. The first difference is that a policeman's real life revolves around criminal law. He has to know exactly what actions are crimes and what evidence can be used to prove them in court. He has to know nearly as much law as a professional lawyer, and what is more, he has to apply it on his feet, in the dark and rain, running down a street after someone he wants to talk to. Little of his time is spent in chatting, he will spend most of his working life typing millions of words on thousands of forms about hundreds of sad, unimportant people who are guilty of stupid, petty crimes. Most television crime drama is about finding the criminal: as soon as he's arrested, the story is over. In real life, finding criminals is seldom much of a problem. Except in very serious eases like murders and terrorist attacks little effort is spent on searching. Having made an arrest, a detective really starts to work. He has to prove his case in court and to do that he often has to gather a lot of evidence. The third big difference between the drama detective and the real one is the unpleasant pressures: first, as members of a police force they always have to behave absolutely in accordance with the law; secondly, as expensive public servants they have to get results. They can hardly ever do both. Most of the time some of them have to break the rules in small ways. If the detective has to deceive the world, the world often deceives him. Hardly anyone he meets tells him the truth. And this separation the detective feels between himself and the rest of the world is deepened by the simplemindedness—as he sees it—of citizens, social workers, doctors, law-makers, and judges, who, instead of eliminating crime punish the criminals less severely in the hope that this will make them reform. The result, detectives feel, is that nine-tenths of their work is recatching people who should have stayed behind bars. This makes them rather cynical.

单选题She has ______ some brilliant scheme to double her income.

单选题" Two hundred eight million, two hundred nine million, two hundred ten million..." That is the sound of solid waste hitting the bottom of garbage cans all over United States in 1996. Solid wastes are materials that are discarded or thrown away after use by consumers and businesses. This does not include fluid materials. During that year, Americans threw away 210 million tons(about 43 pounds/20 kilograms per person daily)of garbage. We throw away 12. 4 million tons of glass and about 80 million tons of paper products. America also throws away large amounts(in tons)of food scraps, yard wastes, plastics, sludge from sewage treatment plants, and other materials. That is almost a mountain of garbage. Even though we make an effort to recycle and compost our solid waste, the amount of how to keep it from polluting our environment. If solid waste is disposed of incorrectly, it can contaminate our surface and underground water supplies. Currently, our municipal waste or waste collected by our cities and towns, goes to landfills. Today, about 85% our garbage goes to landfills or garbage dumps. This waste must be treated to keep rats, flies and other animals from building their home in the landfills. The treat also prevents the growth of bacteria and other organism that carry diseases. So, how do we handle this mountain of garbage? Scientists have come up with different methods for handling our waste problem. One type of waste disposal called sanitary landfill was first used in Fresno California, in 1937. In sanitary landfill, the solid waste is spread in thin layers that compacted and covered with a layer of earth. This is a more expensive method, but it takes away the hazards that are caused by landfills. It also allowed the land to be used for building or recreation. The negative of the landfills is that it's tough to find open land and this process is very expensive. The land also needs its water sources protected so that the water will not pollute the water supply. Landfill(water dumps)and sanitary landfills rely on the natural biodegradability of the solid wastes. Solid wastes are biodegradable if they can decay or break down through the action of living organisms and return to the earth. However certain materials take longer to decay than others, and some materials do not decay or decompose at all. Scientists need to find other methods of waste disposal. Incineration and recycling are methods that are currently in use today.

单选题The report______.poor safety standards for the accident.

单选题Americans are highly ______, and therefore may find it difficult to become deeply involved with others. A. moving B. mobile C. movable D. motional

单选题A radical new bicycle had its first public showing at the National British Cycling Championships in Shrewsbury last weekend. Based on the gold medal- winning design from the Barcelona Olympics, it is the first commercial mountain bike made of a single piece of carbon fibre. Bicycles for amateurs have up to now been made of steel, aluminum or magnesium tubes welded together into the conventional "A-frame" shape. But last year, the British competitor Chris Boardman set world records while winning titles in the Olympic cycling pursuit events on a custom-built, carbon-fibre bicycle with lower weight and wind resistance than standard models. Because carbon fibre is born light and extremely strong, it does not need the A-frame shape, saving further weight Carbon fibre can also be moulded in a single piece, avoiding the weakness of welds. The new bike, which will cost between $ 2000 and $ 3000 when it reaches the shops next month, has the same advantages as the Olympic model, it weighs about 11 kilograms, a saving of 1.5 kilograms on metal frames　 With no crossbar, it has a lower centre of gravity, making it easier to use in race conditions. "When you're doing some aggressive riding, you throw the bike about form side to side," explains Eddie Eccleston, director of British Eagle, a British bicycle manufacturer based in Powys, Wales, which is marketing the bikes. "The low centre of gravity! gives you better control." The frames are being made in the US for British Eagle by SP systems in Camarillo, California, which has clients in the aerospace industry. "This is aerospace technology brought into cycling by enthusiasts," says Eccleston. When professionals tested racing versions of the bike before the Tour de France, they were quicker than metal versions by up to 3 seconds per kilometre. The new design has no struts between the saddle and the back wheel; instead, the frame's flexibility can be "tuned" to individual tastes by changing the mixture of Kevlar fibre and carbon fibre in the back wheel strut, allowing up to 5 centimetres of movement. The carbon-fibre design has a lower centre of gravity and smoother back-wheel suspension than conventional bikes.

单选题In the U.S., the Republican’s doctrines were slightly liberal, whereas the Democrats’ were hardly _____________.