单选题Until about four decades ago, crop yields in agricultural systems depended on (1) resources, recycling organic matter, built-in biological control mechanisms and rainfall patterns. Agricultural yields were (2) but stable. Production was (3) by growing more than one crop or variety in space and time in a field as insurance against pest (4) or severe weather. Inputs of nitrogen were (5) by rotating major field crops with legumes. In turn, rotations suppressed insects, weeds and diseases by effectively (6) the life cycles of these pests. A typical corn belt farmer grew corn (7) with several crops including soybeans, and small grain production was intrinsic to maintain livestock. Most of the labor was done by the family with occasional hired help and no (8) equipment or services were purchased from off4arm sources. In these type of farming systems the link between agriculture and ecology was quite (9) and signs of environment degradation were seldom evident. But as agriculture modernization (10) the ecology-farming linkage was often broken as ecological principles were (11) . In fact, several agricultural scientists have arrived at a (12) consensus that modem agriculture confronts an environment crisis. A growing number of people have become concerned about the long-term (13) of existing food production systems. Evidence has shown that (14) the present capital-and-technology-intensive fanning systems have been extremely productive and competitive, they also bring a (15) of economic, environmental and social problems. Evidence also shows that the very nature of the agricultural structure and prevailing polices have led to this environmental (16) by favoring large farm size, specialized production, crop monocultures and mechanization. Today as more and more farmers are integrated (17) international economies, imperatives to (18) disappear and monocultures are rewarded by economies of scale. In turn, lack of rotations and diversification (19) key self-regulating mechanisms, turning monocultures into highly (20) agro-ecosystems dependent on high chemical inputs.

单选题{{B}}Text 4{{/B}} Artificial hearts have long been the stuff of science fiction. In "Robocop", snazzy cardiac devices are made by Yamaha and Jensen, and in "Star Trek", Jean-Luc Picard, captain of the Enterprise, has one implanted in the year 2328. In the present day, however, their history has been more chequered. The first serious attempt to build one happened in the 1980s, when Jarvik-7, made by Robert Jarvik, a surgeon at the University of Utah, captured the world's attention. But Jarvik-7 was a complicated affair that needed to be connected' via tubes to machines outside the body. The patient could not go home, nor even turn around in bed. Various other designs have been tried since, but all were seen as temporary expedients intended to tide a patient over until the real thing became available from a human donor. That may be about to change. This week, America's Food and Drug Administration gave its approval to a new type of artificial heart made by Abiomed, a firm based near Boston. The agency granted a "humanitarian device exemption", a restricted form of approval that will allow doctors to implant the new device in people whose hearts are about to fail but who cannot, for reasons such as intolerance of the immunosuppressive drugs needed to stop rejection, receive a transplant. Such people have a life expectancy of less than a month, but a dozen similarly hopeless patients implanted with Abiomed's heart survived for about five months. Unlike Dr. Jarvik's device, this newfangled bundle of titanium and polyurethane alms to set the patient free. An electric motor revolving up to 10 000 times a minute pushes an incompressible fluid around the Abiomed heart, and that fluid, in turn, pushes the blood--first to the lungs to be oxygenated, and then around the body. Power is supplied by an electric current generated in a pack outside the body. This induces current in the motor inside the heart. All diagnostics are done remotely, using radio signals. There are no tubes or wires coming out of the patient. The charger is usually plugged into the mains, but if armed with a battery it can be carried around for hours in a vest or backpack, thus allowing the patient to roam freely. Most strikingly, the device's internal battery can last half an hour before it needs recharging. That allows someone time to take a shower or even go for a quick swim without having to wear the charger. Abiomed's chairman, Michael Minogue, does not claim that his firm's product will displace human transplants. Even so, the firm has big ambitions. It is already developing a new version that will be 30% smaller (meaning more women can use it) and will last for five years. That should be ready by 2008--320 years earlier than the writers of "Star Trek" predicted.

单选题The garden looked as if it ______ for years.

单选题Let me tell you a story about Bert and Mildred Bumbridge, who used to be very 1 . For example, Mildred would forget to cook dinner, or Bert would 2 up for work on Sunday 3 it was Monday. One summer they 4 to take a long plane trip. What do 5 suppose happened? Well, they got 6 the airport with only ten minutes to 7 . So time was short. In that situation anyone would 8 the plane right away. But not Mr. and Mrs. Bumbridge. They just had to buy some flight insurance 9 . All in all, who knows what will happen 10 a plane flight? They quickly put some coins into a machine and 11 came their insurance policy. "Who 12 get the money if we 13 , I wonder?" asked Mildred. "My mother, of course," her husband 14 . "We"ll mail the policy to her. Now quickly give me a stamp, 15 you?" he said. "The plane"s going to 16 off in another minute." Bert put the stamp on the envelope, 17 it in the mailbox, and 18 began to cry. What happened, 19 you suppose? He had mailed their 20 to his mother!

单选题Companies can maintain good business relations by Uabiding by/U their promises and agreements.

单选题Walt stayed because ______.

单选题It's not just the sheer accumulation of technology that makes their development so fast; but the cooperation among the members.

单选题{{B}}Passage Two{{/B}} California has a new program called the Digital Textbook Initiative. "Starting this fall with high school math and science, we will be the first state in the nation to provide schools with a state-approved list of digital textbooks. " That was Governor Arnold Schwarzenegger in June,talking about his effort to get schools to use materials available free online. He listed reasons why he thinks digital textbooks make sense. California approves traditional textbooks in six-year cycles. Digital ones can offer the latest information. They lighten the load of school bags. They save paper and trees, and make learning more fun and interactive. And above all, he said, they help schools with their finances. The state has had to make severe cuts in school spending because of deep financial problems. More than six million students attend California public schools. Earlier this year, California invited content developers to offer digital math and science materials for high schools. These had to meet at least 90% of the state's learning requirements.Specially trained teachers examined 16 textbooks and approved ten of them. Six of the ten were published by the CK 12 Foundation, a nonprofit group that had been developing digital science and math books for about two years. The foundation paid teachers and other education professionals to write and edit them. The money came from a group financed by the Khosla Family. California cannot require schools to use the digital textbooks. Individual school districts will have to decide for themselves. Susan Martimo, a California Department of Education official, says she does not expect widespread use right away. Her best guess is that some schools with a lot of technology will be the first to use them, but only in addition to their traditional books. School administrators point out that the texts may be flee online, but students need a way to access them. Not everyone has a computer or electronic reader. Schools could print out copies, but that would not help the environment. Also, there is the cost to train teachers to use digital textbooks effectively.

单选题Why do some desert plants grow tall and thin like organ pipes? Why do most trees in the tropics keep their leaves year round? Why in the Arctic tundra are there no trees at all? After many years without convincing general answers, we now know much about what sets the fashion in plant design. Using terminology more characteristic of a thermal engineer than of a botanist, we can think of plants as mechanisms that must balance their heat budgets. A plant by day is staked out under the Sun with no way of sheltering itself. All day long it absorbs heat. If it did not lose as much heat as it gained, then eventually it would die. Plants get rid of their heat by warming the air around them, by evaporating water, and by radiating heat to the atmosphere and the cold, black reaches of space temperature is tolerable for the processes of life. Plants in the Arctic tundra lie close to the ground in the thin layer of still air that clings there. A foot or two above the ground are the winds of Arctic cold. Tundra plants absorb heat from the Sun and tend to warm up; they probably balance most of their heat budgets by radiating heat to space, but also by warming the still air hat is trapped among them. As long as Arctic plants are close to the ground, they can balance their heat budgets. But if they should stretch up as a tree does, they would lift their working parts, their leaves, into the streaming Arctic winds. Then it is likely that the plants could not absorb enough heat from the Sun to avoid being cooled below a critical temperature. Your heat budget does not balance if you stand tall in the Arctic. Such thinking also helps explain other characteristics of plant design. A desert plant faces the opposite problem from that of an Arctic plant the danger of overheating. It is short of water and so cannot cool itself by evaporation without dehydrating. The familiar sticklike shape of desert plants represents one of the solutions to this problem: the shape exposes the smallest possible surface to incoming solar radiation and provides the largest possible surface from which the plant can radiate heat. In tropical rain forests, by way of contrast, the scorching sun is not a problem for plants because there is sufficient water. This working model allows us to connect the general characteristics of the forms of plants indifferent habitats with factors such as temperature, availability of water, and presence or absence of seasonal differences. Our Earth is covered with a patchwork quilt of meteorological conditions, and the patterns of this patchwork are faithfully reflected by the plants.

单选题A study by scientists in Finland has found that mobile phone radiation can cause changes in human cells that might affect the brain, the leader of the research team said. But Darius Leszczynski, who headed the 2-year study and will present findings next week at a conference in Quebec (魁北克), said more research was needed to determine the seriousness of the changes and their impact on the brain or the body. The study at Finland's Radiation and Nuclear Safety Authority found that exposure to radiation from mobile phones can cause increased activity in hundreds of proteins in human cells grown in a laboratory, he said. "We know that there is some biological response. We can detect it with our very sensitive approaches, but we do not know whether it can have any physiological effects on the human brain or human body," Leszczynski said. Nonetheless, the study, the initial findings of which were published last month in the scientific journal Differentiation, raises new questions about whether mobile phone radiation can weaken the brain's protective shield against harmful substances. The Study focused on changes in cells that line blood vessels and on whether such changes could weaken the functioning of the blood-brain barrier, which prevents potentially harmful substances from entering the brain from the bloodstream, Leszczynski said. The study found that a protein called hsp27 linked to the functioning of the blood-brain barrier showed increased activity due to irradiation and pointed to a possibility that such activity could make the shield more permeable(能透过的), he said. "Increased protein activity might cause cells to shrink—not the blood vessels but the cells themselves—and then tiny gaps could appear between those cells through which some molecules could pass," he said. Leszczynski declined to speculate on what kind of health risks that could pose, but said a French study indicated that headache, fatigue and sleep disorders could result. "These are not life-threatening problems but can cause a lot of discomfort," he said, adding that a Swedish group had also suggested a possible link with Alzheimer's disease. "Where the truth is, I do not know," he said. Leszczynski said that he, his wife and children use mobile phones', and he said that he did not think his study suggested any need for new restrictions on mobile phone use.

单选题Stress makes a person want to stop whatever they are doing, try to relax, and become calm again. Too much stress results in physical, emotional, and mental health problems. There are numerous physical effects of stress. Stress can affect the heart. It can increase the pulse rate, make the heart miss beats, and can cause high blood pressure. Stress can affect the respiratory system. It can lead to asthma. It can cause a person to breathe too fast, resulting in a loss of important carbon dioxide. Stress can affect the stomach. It can cause stomach aches and problems digesting food. These are only a few examples of the wide range of illnesses and symptoms resulting from stress. Emotions are also easily affected by stress. People suffering from stress often feel anxious. They may have panic attacks. They may feel tired all the time. When people are under stress, they often overreact to little problems. For example, a normally gentle parent under a lot of stress at work may yell at a child for dropping a glass of juice. Stress can make people angry, moody, or nervous. Long-term stress can lead to a variety of serious mental illnesses. Depression, an extreme feeling of sadness and hopelessness, can be the result of continued and increasing stress. Alcoholism and other addictions often develop as a result of overuse of alcohol or drugs to try to relieve stress. Eating disorders, such as anorexia, are sometimes caused by stress and are often made worse by stress. If stress is allowed to continue, then one"s mental health is put at risk. It is obvious that stress is a serious problem. It attacks the body. So, reduce stress: stop the world and rest for a while.

单选题The details of the geological history of the Rocky Mountains have been lost______hundreds of millions of years.

单选题For many people today, reading is no longer relaxation. To keep up their work they must read letters, reports, trade publications, interoffice communications, not to mention newspapers and magazines: a never-ending flood of words. In 21 a job or advancing in one, the ability to read and comprehend 22 can mean the difference between success and failure. Yet the unfortunate fact is that most of us are 23 readers. Most of us develop poor reading 24 at an early age, and never get over them. The main deficiency 25 in the actual stuff of language itself ——words. Taken individually, words have 26 meaning until they are strung together into phrases, sentences and paragraphs. 27 , however, the untrained reader does not read groups of words. He laboriously reads one word at a time, often regressing(退回) to 28 words or passages. Regression, the tendency to look back over 29 you have just read, is a common bad habit in reading. Another habit which 30 down the speed of reading is vocalization―sounding each word either orally or mentally as 31 reads. To overcome these bad habits, some reading clinics use a device called an 32 , which moves a bar (or curtain) down the page at a predetermined(预先确定的) speed. The bar is set at a slightly faster rate 33 the reader finds comfortable, in order to "stretch" him. The accelerator forces the reader to read fast, 34 word-by-word reading, regression and subvocalization(默读)practically impossible. At first 35 is sacrificed for speed. But when you learn to read ideas and concepts, you will not only read faster, 36 your comprehension will improve. Many people have found 37 reading skill drastically improved after some training. 38 Charlce Au, a business manager, for instance, his reading rate was a reasonably good 172 words a minute 39 the training, now it is an excellent 1,378 words a minute. He is delighted that how he can 40 a lot more reading material in a short period of time.

单选题Many people imagine that Alzheimer"s disease, the degenerative disorder that ultimately leaves sufferers with total memory loss, is an inevitable result of aging. This is not so. 【C1】______the risks of contracting the disease increase with age, there are many elderly people【C2】______memories are perfect. Most of us are so ill-【C3】______about all forms of memory loss that we label everything "Alzheimer"s". Alzheimer"s disease itself can【C4】______people as young as 30 and can progress either quickly or slowly. It can also【C5】______the blame for other non-degenerative conditions such as deep depression. 【C6】______, only an examination of the brain tissue during all autopsy can produce an accurate【C7】______of the disease. The causes of Alzheimer"s are unknown. They may be either【C8】______or environmental. A study in 1996 of 13, 000 people whose parents or siblings had the disease showed they had five times【C9】______chance of succumbing【C10】______the age of 80 than those with no family【C11】______of the problem. There are other factors, however. In a study of identical twins, it was found that only about half of the twin pairs developed Alzheimer"s and, when both twins【C12】______it, they did so as【C13】______as 15 years apart. The possibility【C14】______environment plays a part was【C15】______by another 1996 study, this time of two groups of elderly Japanese men. One group lived in Hawaii, the other in Japan. The Hawaiian group had a much higher【C16】______of the disease. Aluminum has been blamed for, the development of Alzheimer"s. This is because a high level of aluminum has been found in the brains of sufferers. The disease was first diagnosed at the beginning of the 20th century. It was at this time【C17】______aluminum was becoming widely available for use in cooking pots. Memory loss, difficulty in【C18】______familiar tasks, and problems with abstract thinking are all【C19】______of the onset of the disease. One unusual feature is its impact on language. It attacks nouns first, 【C20】______verbs. Grammar is one of the last things to go.

单选题Officials are supposed to ____ themselves to the welfare and health of the general public.

单选题If I correct someone, I will do it with as much good humor and self-restraint as if I were the one ______. A. correcting B. to correct C. to be corrected D. being corrected

单选题He is used to flying by air and on no occasion ______ frightened. A) he has ever felt B) he ever feels C) ever does he feel D) has he ever felt

单选题(Despite of) (many) attempts (to introduce) a universal language, notably Esperanto and Idiom Neutral(世界语和人造语言), the effort has met with very (little) success.