单选题How does Organisms Ward off Invaders The livelihood of each species in the vast and intricate assemblage of living things depends on the existence of other organisms. This interdependence is sometimes subtle, some times obvious. Perhaps the most straightforward dependence of one species on another occurs with parasites, organisms that live on or in other living things and derive nutrients directly from them. The parasitic way of life is widespread. A multitude of microorganisms (including viruses and bacteria) and an army of invertebrates or creatures lacking a spinal column (including crustaceans, insects, and many different types of worms) make their livings directly at the expense of other creatures. In the face of this onslaught, living things have evolved a variety of defense mechanisms for protecting their bodies from invasion by other organisms. Certain fungi and even some kinds of bacteria secrete substances known as antibiotics into their external environment. These substances are capable of killing or inhibiting the growth of various kinds of bacteria that also occupy the area, thereby eliminating or reducing the competition for nutrients. The same principle is used in defense against invaders in other groups of organisms. For example, when attacked by disease-causing fungi or bacteria, many kinds of plants produce chemicals that help to ward off the invaders. Members of the animal kingdom have developed a variety of defense mechanisms for dealing with parasites. Although these mechanisms vary considerably, all major groups of animals are capable of detecting and reacting to the presence of "foreign" cells. In fact, throughout the animal kingdom from sponges to certain types of worms shellfish, and all vertebrates (creatures possessing spinal column), there is evidence that transplants of cells or fragments of tissues into an animal are accepted only if they come from genetically compatible or closely related individuals. The ability to distinguish between "self" and "non-self", while present in all animals, is most efficient among vertebrates. which have developed an immune system as their defense mechanism. The immune system recognizes and takes action against foreign invaders and transplanted tissues that are treated as foreign cells.

单选题The Sahara The name Sahara derives from the Arabic word for "desert" or "steppe". At 3.5 million square miles, an area roughly the size of the United States, the Sahara Desert in northern Africa is the largest desert in the world. It spans the continent from the Atlantic Ocean to the Red Sea. Daytime temperatures can reach as high as 130~F. The humidity sometimes gets into the teens. But it can also be as low as 2.5 percent, the lowest in the world. Most of the Sahara receives less than five inches of rain per year, while large areas sometimes have no rainfall at all for years. At the heart of the Sahara is the landlocked north African country of Niger. Here the sand dunes can be 100 feet tall and several miles long. Here sand plains stretch over an area larger than Germany where there is neither water nor towns. Yet sitting in the midst of the surrounding desert is the town of Bilma. Suddenly there are pools of clear water. Surprisingly, there are groves of date palms. Underground water resources, or oases, sufficient to support irrigated agriculture are found in dry stream beds and depressions. Irrigation ditches run off a creek to water fields. Corn, cassava, tea, peanuts, hot peppers, and orange, lime, and grapefruit trees grow in these fields. Donkeys and goats graze on green grass. The Sahara of Niger is still a region where you can see a camel caravan of 500 camels tied together in loose lines as long as a mile, traveling toward such oasis towns. There a caravan will collect life-sustaining salt, which is mined from watery basins, and transport it up to 400 miles back to settlements on the edges of the desert. The round trip across the vast sands takes one month.

单选题It took more than two years to build "The Castle Mall".

单选题The phrase "make room" in the last paragraph could be best replaced by

单选题Her father was a quiet man with graceful manners.

单选题This poem Udepicts/U the beautiful scenery of a small town in the South.

单选题The following may be the reasons why the librarian does not want to help his friend EXCEPT that

单选题Although originally a German innovation, kindergarten got its real start in the United States as a movement to provide an improved learning environment for children.

单选题Nursing-home For an increasing number of students at American universities, old is suddenly in. The reason is obvious: the graying of America means jobs. Coupled with the aging of the baby-boom (生育高峰) generation, a longer life span means that the nation's elderly population is bound to expand significantly over the next 50 years. By 2050, 25 percent of all Americans will be older than 65, up from 14 percent in 1995. The change poses profound questions for government and society, of course. But it also creates career opportunities in medicine and health professions, and in law and business as well. "In addition to the doctors, we're going to need more sociologists, biologists, urban planners and specialized lawyers," says Professor Edward Schneider of the University of Southern California's (USC School of Gerontology, 老年学). Lawyers can specialize in "elder law," which covers everything from trusts and estates to nursing-home abuse and age discrimination. Businessmen see huge opportunities in the elder market because the baby boomers, 74 million strong, are likely to be the wealthiest group of retirees in human history. "Any student who combines an expert knowledge in gerontology with an MBA or law degree will have a license to print money," one professor says. Margarite Santos is a 21-year-old senior at USC. She began college as a biology major but found she was "really bored with bacteria." So she took a class in gerontology and discovered that she liked it. She says, "I did volunteer work in retirement homes and it was very satisfying./

单选题We can no longer Utolerate/U his actions.

单选题I catch cold now and then. A. always B. occasionally C. constantly D. regularly

单选题He looks like a {{U}}crazy{{/U}} man.

单选题The First Settlement in North America It is very difficult to say that when colonization began. The first hundred years after Christopher Columbus"s journey of discovery in 1492 did not produce any settlement on the North American continent but rather some Spanish trading posts further south, a great interest in gold and adventure, and some colorful crimes in which the English had their part. John Cabot, originally from Genoa but a citizen of Venice, was established as a trader in Bristol, England, when he made a journey in 1497. But his ship, the Matthew, with its crew of eighteen, did no more than see an island (probably off the New England coast) and return home. He and his son made further voyages across the north Atlantic, which enabled the English Crown to claim a "legal" title to North America. But for a long time afterwards the Europeans" interest in America was mainly confined to the Spanish activities further south. The first beginning of permanent settlement in North America was nearly a hundred years after Columbus"s first voyage. The Englishman Sir Waiter Raleigh claimed the whole of North America for England, calling it Virginia. In 1585 he sent a small group of people who landed in Roanoke Island, but they stayed only for a year and then went back to England with another expedition, led by Drake, in 1587. A second group who landed in 1587 had all disappeared when a further expedition arrived in 1590. The first permanent settlement in North America was in 1607. English capitalists founded two Virginia companies, a southern one based in London and a northern one based in Bristol. It was decided to give the name New England to the northern area. The first settlers in Virginia were little more than wage slaves to the company. All were men and the experiment was not very successful. Many died. Those who survived lived in miserable conditions. By 1619 the colony had only a thousand people.

单选题Until the late nineteenth century,there was no uniform system of time-keeping in the United States.

单选题Mary felt lonely after her husband died in a car accident.A. aloneB. gloomyC. desolateD. separate

单选题下面的短文有15处空白，请根据短文内容为每处空白确定1个最佳选项。 Sending E-mails to Professors One student skipped class and then sent the professor an e-mail {{U}}(51) {{/U}} for copies of her teaching notes. Another {{U}}(52) {{/U}} that she was late for a Monday class because she was recovering from drinking too much at a wild weekend party. At colleges and universities in the US, e-mail has made professors more approachable(平易近人 ). But many say it has made them too accessible, {{U}}(53) {{/U}} boundaries that traditionally kept students at a healthy distance. These days, professors say, students seem to view them as available {{U}}(54) {{/U}} the clock, sending a steady stream of informal e-mails. "The tone that they take in e-mails is pretty astounding(令人吃惊的)." said Michael Kessler, an assistant dean at Georgetown University. "They'll {{U}}(55) {{/U}} you to help: 'I need to know this. '" "There's a fine {{U}}(56) {{/U}} between meeting their needs and at the same time maintaining a level of legitimacy (正统性) as an {{U}}(57) {{/U}} who is in charge. " Christopher Dede, a professor at the Harvard Graduate School of Education, said {{U}}(58) {{/U}} show that students no longer defer to (听从) their professors, perhaps because they realize that professors' {{U}}(59) {{/U}} could rapidly become outdated. "The deference was driven by the notion {{U}}(60) {{/U}} that professors were all-knowing sources of deep knowledge. " Dede said, and that notion has weakened {{U}}(61) {{/U}}. For junior faculty members, e-mails bring new tension into their work, some say, as they struggle with how to {{U}}(62) {{/U}}. Their job prospects, they realize, may rest in part on student evaluations of their accessibility. College students say e-mail makes {{U}}(63) {{/U}} easier to ask questions and helps them learn. But they seem unaware that what they write in e-mails could have negative effects on {{U}}(64) {{/U}} them, said Alexandra Lahav, and associate professor of Law at the University of Connecticut. She recalled an e-mail message from a student saying that he planned to miss class so he could play with his son. Professor Lahav did not respond. "Such e-mails can have consequences. " she said. "Students don't understand that {{U}}(65) {{/U}} they say in e-mail can make them seem unprofessional, and could result in a bad recommendation. "

单选题Brotherly Love Adidas and Puma have been two of the biggest names in sports shoe manufacturing for over half a century. Since 1928 they have supplied shoes for Olympic athletes, World Cup-winning football heroes, Muhammad Ali, hip hop stars and rock musicians famous all over the world. But the story of these two companies begins in one house in the town of Herzogenaurach, Germany. Adolph and Rudolph Dassler were the sons of a shoemaker. They loved sport but complained that they could never find comfortable shoes to play in. Rudolph always said, 'You cannot play sports wearing shoes that you'd walk around town with.' So they started making their own. In 1920 Adolph made the first pair of athletics shoes with spikes(钉)，produced on the Dasslers' kitchen table. On lst July 1924 they formed a shoe company, Dassler Brothers Ltd and they worked together for many years. The company became successful and it provided the shoes for Germany's athletes at the 1928 and 1932 Olympic Games. But in 1948 the brothers argued. No one knows exactly what happened, but family members have suggested that the argument was about money or women. The result was that Adolph left the company. His nickname was Adi, and using this and the first three letters of the family name, Dassler, he founded Adidas. Rudolph relocated across the River Aurach and founded his own company too. At first he wanted to call it Ruda, but eventually he called it Puma, after the wild cat. The famous Puma logo of the jumping cat has hardly changed since. After the big split of 1948 Adolph and Rudolph never spoke to each other again and their companies have now been in competition for over sixty years. Both companies were for many years the market leaders, though Adidas has always been more successful than Puma. A hip hop group, Run DMC, has even written a song called "My Adidas" and in 2005 Adidas bought Reebok, another big sports shoe company. The terrible family argument should really be forgotten, but ever since it happened, over sixty years ago, the town has been split into two. Even now, some Adidas employees and Puma employees don't talk to each other.

单选题Large Thighs" May Protect Heart" Men and women with thighs over 60cm(23.6in)in circumference have a lower risk of heart disease and early death ,a study of 3,000 people suggests. The relationship remains even when body fat, smoking and blood cholesterol are taken into account, a Danish team says. Those with narrow thighs may not have enough muscle mass to deal with insulin properly, raising the risk of diabetes and, in turn, heart disease, they say. Some said it was too early to change current advice on eating and exercise for heart health. The study ,published in the British Medical Journal, followed men and women in Denmark for more than 10 years. They were measured for height, weight and thigh, hip and waist circumference and their overall percentage of body fat was calculated. The thigh measurement was taken just below the gluteal fold, which is the crease caused by your buttocks. Researchers also looked at the activity levels of the participants, whether they smoked, their blood pressure and cholesterol levels. They then monitored incidence of heart disease over 10 years and death rates over 12 - and - a - half years. The team at the Copenhagen University Hospital found that those with the smallest thighs—be- low 55cm—had twice the risk of early death or serious health problems. Professor Befit Heitmann, who led the research, said:" The increased risk was independent of abdominal and general obesity and lifestyle and cardiovascular risk factors such as blood pressure. " "Additionally we found that the risk was more highly related to thigh circumference than to waist circumierence. " "The nice thing is that if you have a small thigh you call do something about it through exercise. " Previous studies have suggested that a waist circumference of over 35in(88.9cm) for a woman and 40in(101.6era) for a man indicated a high risk of developing diabetes and heart disease. Professor Heitmann's team says the risk of narrow thighs could be associated with too little muscle mass. They say this can lead to the body not responding to insulin properly, increasing the risk of type 2 diabetes and, in the long- run, heart disease.

单选题The attitude of the author towards the research project is

单选题Taking a Dim View of Solar Energy Despite the bad economy, or maybe because of it, the rooftop - solar industry is booming, as Americans become increasingly intrigued by the idea of turning their roofs into mini power plants and cutting their electric bills. In 2008,33,500 rooftop solar systems were installed in the United States, a 63 percent increase over the amount of capacity installed in 2007. In California, the solar capital of country, the increase was 95 percent. Meanwhile ,the outlook for the other side of the solar industry—the large, centralized power plants—isn't so sunny. These megaprojects—acres of desert covered in thousands of solar panels sending electricity—controlled mostly by utility companies that have had a monopoly over the country's electricity grid, were supposed to be the key to the future of the solar industry. So far, they're getting vastly outpaced by the decentralized rooftop approach. According to the Interstate Renewable Energy Council's 2006—2008 count, consumers added 522 megawatts to the grid; whereas utility Companies added just 96 megawatts. The disparity has utilities worried about loosing their grip on the country's energy industry, and the $130 billion residential electricity market. In some cases, utilities are actually taking direct steps to thwart rooftop solar. "There is a tension between distributed solar generation and utilities," says Adam Browning, executive director of The Vote Solar Initiative, a solar advocacy group in San Francisco. "They've had the energy pie to themselves for a century, and now facing a future where clean distributed energy will play a large part, they're looking for ways to profit from it and maintain control. People want solar panels on their roofs, so utilities should be working to make that happen rather than getting in the way. "says Browning. It's not hard to understand why a big utility might not like the idea of homes and buildings being covered in solar panels. If every building in America is generating its own solar energy, that throws a big wrench into their business model. But as most states have passed renewable - energy standards recently, mandating that a certain percentage of their energy come from renewable sources, utilities have become reluctant players in the solar game because, frankly, they have no choice. However, thanks to state and federal government subsidies, private sector can seize this opportunity to grow.