求y""-7y"+12y=x满足初始条件y(0)=的特解.

求微分方程y""+2y"-3y=e x +x的通解．

已知方程y""+p(x)y"+g(x)y=0，求证： (I)若p(x)+xq(x)≡0，则y=x是方程的一个特解； (Ⅱ)若m 2 +mp(x)+1(x)≡0，则y=e mx 是方程的一个特解．

设三阶常系数齐次线性微分方程有特解y 1 =e x ，y 2 =2xe x ，y 3 =3e 一x ，则该微分方程为( )．

函数y=Cx+(其中C是任意常数)对微分方程=x而言，()

求微分方程y"+4y′+4y=e ax 的通解．

求方程2x－y=－x2的通解．

单选题When Rupert Murdoch sees beams of light in the American advertising market, it is not necessarily time to reach for the sunglasses. Last October, when the impact of September 11th was only beginning to tell, the boss of NASCAR, a media group, had already identified " strong rays of sunshine". With ad sales still languishing, Mr. Murdoch declared last month that " there are some hints of a modest upswing in tile US advertising market". His early optimism turned out to be misplaced. Now, however, other industry observers are beginning to agree with him. Advertising usually exaggerates the economic cycle, falling sharply and early in a downturn, and rebounding strongly once the economy has begun to recover. This is because most managers prefer to trim their ad budgets rather than their payrolls, and restore such spending only once they feel sure that things are looking up. Last year, America's ad market shrank by 9. 8% , according to CMIR, a research firm. Although ad spending has not yet recovered across all media, some analysts now expect overall ad spending to start to grow in the third quarter. The signs of improvement are patchy, however. Ad spending on radio and television seems to be inching up—advertising on American National Radio was up 2% in January on the same period last year, according to Aegis—while spending on magazines and newspapers is still weak. Even within any one market, there are huge differences; just pick up a copy of one of the now-slimline high-teeh magazines that once bulged with ads, and compare it with the hefty celebrity or women's titles. Advertisers in some categories, such as the travel industry, are still reluctant to buy space or airtime, while others, such as the car and movie businesses, have been bolder. The winter Olympics, held last month in Salt Lake City, has also distorted the spending on broadcast advertising in the first quarter. Nonetheless, there is an underlying pattern. One measure is the booking of ad spots for national brands on local television. By early March, according to Mr. Westerfield's analysis, such bookings were growing fast across eight out of the top ten advertising sectors, led by the financial and motor industries. UBS Warburg now expects the " upfront" market, which starts in May when advertisers book advance ad spots on the TV networks for the new season in September, to be up 4% on last year. On some estimates, even online advertising could pick up by the end of the year.

单选题What's your earliest childhood memory? Can you remember learning to walk? Or talk? The first time you heard thunder or watched a television program? Adults seldom (1) events much earlier than the year or so before entering school, (2) children younger than three or four (3) retain any specific, personal experiences. A variety of explanations have been (4) by psychologists for this "childhood amnesia". One argues that the hippo-campus; the region of the brain which is (5) for forming memories, does not mature until about the age of two. But the most popular theory (6) that, since adults don't think like children, they cannot (7) childhood memories. Adults think in words, and their life memories are like stories or (8) one event follows (9) as in a novel or film. But when they search through their mental (10) for early childhood memories to add to this verbal life story, they don't find any that fit the (11) . It's like trying to find a Chinese word in an English dictionary. Now psychologist Annette Simms of the New York State University offers a new (12) for childhood amnesia. She argues that there simply aren't any early childhood memories to (13) . According to Dr. Simms, children need to learn to use someone else's spoken description of their personal (14) in order to turn their own short-term, quickly forgotten (15) of them into long-term memories. In other (16) , children have to talk about their experiences and hear others talk about (17) --Mother talking about the afternoon (18) looking for seashells at the beach or Dad asking them about their day at Ocean Park. Without this (19) reinforcement, says Dr. Simms, children cannot form (20) memories of their personal experiences.Notes: childhood amnesia 儿童失忆症。

单选题Though it is mere 1 to 3 percent of the population, the upper class possesses at least 25 percent of the nation's wealth. This class has two segments: upper-upper and lower-upper. Basically, the upper-upper class is the "old rich"—families that have been wealthy for several generations—an aristocracy of birth and wealth. Their names are in the Social Register, a listing of acceptable members of high society. A few are known across the nation, such as the Rockefellers, Roosevelts, and Vanderbilts. Most are not visible to the general public. They live in grand seclusion, drawing their income from the investment of their inherited wealth. In contrast, the lower-upper class is the "new rich". Although they may be wealthier than some of the old rich; the new rich have hustled to make their money like everybody else beneath their class. Thus their prestige is generally lower than that of the old rich, who have not found it necessary to lift a finger to make their money, and who tend to look down upon the new rich. However its wealth is acquired, the upper class is very, very rich. They have enough money and leisure time to cultivate an interest in the arts and to collect rare books, painting, and sculpture. They generally live in exclusive areas, belong to exclusive social clubs, communicate with each other, and marry their own kind—all of which keeps them so distant from the masses that they have been called the out-of-sight class. More than any other class, they tend to be conscious of being members of a class. They also command an enormous amount of power and influence here and a broad, as they hold many top government positions, run the Council on Foreigh Relations, and control multinational corporations. The actions affect the lives of millions.

单选题Walt Disney could have built his biggest theme park anywhere. He chose Florida. The weather is balmy, and when it gets too hot there are lots of pools to cool off in, says. Meg Crofton, Walt Disney World's CEO'. Florida also offers plenty of space to expand. Disney World, which was first carved out of wild woodland in 1971, has swollen to four parks covering 40 square miles ( 104 sq km) and employing 60 000 "cast members". Contrary to the stereotype of rapid flow in the service sector, the average full-time employee sticks around for nine years. Florida's business climate is sunny, too. The Milken Institute, a think-tank in California, compiles an index of "best-performing cities" in America, a composite measure of such things as job creation, wage growth and whether businesses are thriving. In the most recent index, six of the top ten metropolitan areas are in Florida. ( Orlando-Kissimmee is sixth. ) And 18 of the top 30 are in the South. For a long time the South's weather got in the way of its development. Richard Pillsbury, a geography professor at Georgia State University, describes traditional life in the lowland South, a region stretching from northern Virginia down to the Gulf coast of Texas: "Smallish barren farms almost lost in the white heat of a hot and humid summer sun as the owners and their help fought swarms of mosquitoes to plant, cultivate and harvest the meagre cotton crop for market." Then air-conditioning came. As it spread after the World War Ⅱ, the South became suddenly more comfortable to live and work in. From the 1940s until the 1980s the region boomed. In his book Old South, New South, Gavin Wright lists four reasons why Federal defence spending stimulated growth. Sunshine attracted skilled professionals. The South, having developed so little in the past, was a "clean slate", without strong labour unions, entrenched bureaucracies, restrictive laws or outdated machinery. Lastly, given how much catching up the South had to do, the potential returns were higher than in the north. Southerners have prospered in part by playing to their traditional strengths. The fame of southern hospitality has bolstered the region's hotel chains, such as Holiday Inn. That of southern cuisine helps local restaurants, such as Waffle House, Cracker Barrel and KFC. Arkansas-based Wal-Mart, the world's largest retailer, has kept costs low by refusing to recognize unions. And Coca-Cola owes at least some of its success to its southern origins.

单选题Time spent in a bookshop can be most enjoyable, whether you are a book-lover or merely there to buy a book as a present. You may even have entered the shop just to find shelter from a sudden shower. But the desire to pick up a book with an attractive dust-jacket is irresistible. You soon become absorbed in some book or other, and usually it is only much later that you realize that you have spent far too much time there. This opportunity to escape the realities of everyday life is, I think, the main attraction of a bookshop. There are not many places where it is possible to do this. A music shop is very much like a bookshop. You can wander round such places to your heart's content. If it is a good shop, no assistant will approach you with the inevitable greeting: "Can I help you, sir?" You needn't buy anything you don't want. In a bookshop an assistant should remain in the background until you have finished browsing. Then, and only then, are his services necessary. You have to be careful not to be attracted by the variety of books in a bookshop. It is very easy to enter the shop looking for a book on, say, ancient coins and to come out carrying a copy of the latest best-selling novel and perhaps a book about brass-rubbing -- something which had only vaguely interested you up till then. This volume on the subject, however, happened to be so well illustrated and the part of the text you read proved so interesting that you just had to buy it. This sort of thing can be very dangerous. Booksellers must be both long suffering and indulgent. There is a story which wei1 illustrates this. A medical student had to read a textbook which was far too expensive for him to buy. He couldn't obtain it from the library and the only copy he could find was in his bookshop. Every afternoon, therefore, he would go along to the shop and read a little of the book at a time. One day, however, he was dismayed to find the book missing from its usual place and about to leave when he noticed the owner of the shop beckoning to him. Expecting to be reproached, he went toward him. To his surprise, the owner pointed to the book, which was tucked away in a corner. "I put it there in case anyone was tempted to buy it," he said, and left the delighted student to continue his reading.

单选题When the United States and Korea(SOK) announced their new free-trade agreement last month, the news was mainly economic. The deal would give American farmers and bankers alike better access to Korean consumers and help Korean companies push more electronics, cars and textiles into the United States. Largely unreported was the political angle--the U.S.-Korea(SOK) free trade agreement comes at precisely the moment when America's military presence on the Korean Peninsula is rapidly diminishing, anti-U.S. nationalism in Korea(SOK) is growing and China is playing an ever more important leadership role in the region. This FTA is much more significant in strategic than economic terms. It is the same about any number of trade deals in Asia these days. While free-trade agreements have always been somewhat political, solidifying national relationships, the use of FTAs in geopolitical jockeying(竞赛) is reaching new heights in East Asia. Since 1997, the number of FTAs in the region has risen from seven to 38. Last time we saw this sort of frenzied bilateral activity was back in the 1930s. That worries some economists, who fear that all the free-trade politicking will further erode an already beleaguered global trading system, and create a snowball effect of countermeasures. It's no accident that the activity in the region has increased since 2004, which marked the beginning of a massive free trade agreement between China and the Association of Southeast Asian Nations. China offered countries like Laos and Cambodia an "early harvest," unilaterally opening up markets for hundreds of different kinds of agricultural products. That in turn helped smooth the way for a reduction in tension in hot spots like the disputed South China Sea territories. FTAs are becoming a key instrument for great-power diplomacy. That worries rivals, who are rushing to find their own partners. The Japanese, for example, have always been cautious when it comes to bilateral agreements. Japanese Prime Minister Shinzo Abe recently announced a new push for more Japanese FTAs in the region. Meanwhile, the EU is trying desperately to push its way back into the region, recently announcing plans to negotiate its own deals with both South Korea and the ASEAN nations. How will all the wheeling and dealing end? Not with more efficient trading. A recent map of Asian trade deals shows an increasingly complicated "spaghetti bowl" hindering broader global efforts to liberalize trade. Such deals have a disproportionately negative effect on small and medium-sized enterprises, representing as much as 80 percent of jobs in some parts of Asia. Already, the U.S.-Korea(SOK) deal is causing grousing(不满) in Japan, which would take a hit as Korean competitors no longer have. to deal with U.S. tariffs. Still, that probably won't turn the tide -- the most important criterion in motivating a country to seek FTAs, well ahead of economic reform, was--surprise --politics.

单选题Every second, 1 hectare of the world's rainforest is destroyed. That's equivalent to two football fields. An area the size of New York City is lost every day. In a year, that adds up to 31 million hectares--more than the land area of Poland. This alarming rate of destruction has serious consequences for the environment; scientists estimate, for example, that 137 species of plant, insect or animal become extinct every day due to logging. In British Columbia, where, since 1990, thirteen rainforest valleys have been clearcut, 142 species of salmon have already become extinct, and the habitats of grizzly bears, wolves and many other creatures are threatened. Logging, however, provides jobs, profits, taxes for the government and cheap products of all kinds for consumers, so the government is reluctant to restrict or control it. Much of Canada's forestry production goes towards making pulp and paper. According to the Canadian Pulp and Paper Association, Canada supplies 34% of the world's wood pulp and 49% of its newsprint paper. If these paper products could be produced in some other way, Canadian forests could be preserved. Recently, a possible alternative way of producing paper has been suggested by agriculturalists and environmentalists: a plant called hemp. Hemp has been cultivated by many cultures for thousands of years. It produces fiber which can be made into paper, fuel, oils, textiles, food, and rope. For many centuries, it was essential to the economies of many countries because it was used to make the ropes and cables used on sailing ships; colonial expansion and the establishment of a world wide trading network would not have been possible without hemp. Nowadays, ships' cables are usually made from wire or synthetic fibres, but scientists are now suggesting that the cultivation of hemp should be revived for the production of paper and pulp. According to its proponents, four times as much paper can be produced from land using hemp rather than trees, and many environmentalists believe that the large-scale cultivation of hemp could reduce the pressure on Canada's forests. However, there is a problem : hemp is illegal in many countries of the world. This plant, so useful for fiber, rope, oil, fuel and textiles, is a species of cannabis, related to the plant from which marijuana is produced. In the late 1930s, a movement to ban the drug marijuana began to gather force, resulting in the eventual banning of the cultivation not only of the plant used to produce the drug, but also of the commercial fiber-producing hemp plant. Although both George Washington and Thomas Jefferson grew hemp in large quantities on their own land, any American growing the plant today would soon find himself in prison--despite the fact that marijuana cannot be produced from the hemp plant, since it contains almost no THC (the active ingredient in the drug). In recent years, two major movements for legalization have been gathering strength. One group of activists believes that ALL cannabis should be legal--both the hemp plant and the marijuana plant--and that the use of the drug marijuana should not be an offense. They argue that marijuana is not dangerous or addictive, and that it is used by large numbers of people who are not criminals but productive members of society. They also point out that marijuana is less toxic than alcohol or tobacco. The other legalization movement is concerned only with the hemp plant used to produce fiber; this group wants to make it legal to cultivate the plant and sell the fiber for paper and pulp production. This second group has had a major triumph recently: in 1997, Canada legalized the farming of hemp for fiber. For the first time since 1938, hundreds of farmers are planting this crop, and soon we can expect to see pulp and paper produced from this new source.

问答题Directions:Writeanessayof160—200wordsbasedonthefollowingphoto.Inyouressay,youshould1)describethephotobriefly,2)illustratethegoodofvolunteerworkwith(a)specificexample(s),and3)makeyoursuggestion(s)tofindvolunteerwork.YoushouldwriteitneatlyonANSWERSHEET2.

问答题Practically speaking, the artistic maturing of the cinema was the single-handed achievement of David W. Griffith (1875-1948). (46)Before Griffith, photography in dramatic films consisted of little more than placing the actors before a stationary camera and showing them in full length as they would have appeared on stage. From the beginning of his career as a director, however, Griffith, because of his love of Victorian painting, employed composition. He conceived of the camera image as having a foreground and a rear ground, as well as the middle distance preferred by most directors. By 1910 he was using close-ups to reveal significant details of the scene or of the acting and extreme long shots to achieve a sense of spectacle and distance. His appreciation of the camera' s possibilities produced novel dramatic effects. (47) By splitting an event into fragments and recording each from the most suitable camera position, he could significantly vary the emphasis from camera shot to camera shot. Griffith also achieved dramatic effects by means of creative editing. By juxtaposing images and varying the speed and rhythm of their presentation, he could control tile dramatic intensity of the events as the story progressed. (48) Despite the reluctance of his producers, who feared that the public would not be able to follow a plot that was made up of such juxtaposed images, Griffith persisted, and experimented as well with other elements of cinematic syntax that have become standard ever since. These included the flashback, permitting broad psychological and emotional exploration as well as narrative that was not chronological, and the crosscut between two parallel actions to heighten suspense and excitement. In thus exploiting fully the possibilities of editing, Griffith transposed devices of the Victorian novel to film and gave film mastery of time as well as space. Besides developing the cinema's language, Griffith immensely broadened its range and treatment of subjects. (49) His early output was remarkably eclectic: it included not only the standard comedies, melodramas, westerns, and thrillers, but also such novelties as adaptations from Browning and Tennyson, and treatments of social issues. As his successes mounted, his ambitions grew, and with them the whole of American cinema. When he remade Enoch Arden in 1911, he insisted that a subject of such importance could not be treated in the then conventional length of one reel. Griffith' s introduction of the American-made multi-reel picture began an immense revolution. Two years later, Judith of Bethulia, an elaborate historic philosophical spectacle, reached the unprecedented length of four reels, or one hour' s running time. (50) From our contemporary viewpoint, the pretensions of this film may seem a little ridiculous, but at the time it provoked endless debate and discussion and gave a newintellectual respectability to the cinema.

问答题Directions:Writeanessayof160-200wordsbasedonthefollowingdrawing.Inyouressay,youshould1)describethedrawingbriefly,2)explainitsintendedmeaning,andthen3)giveyoursuggestionsastothebestwaytoencouragehonesty.YoushouldwriteneatlyonANSWERSHEET2.诚信如照镜子，你以真面目对它，它报以真面目，你以假面目对它，它也还你假面目。

填空题差分方程y x+1 一y x =x2 x 的通解为___________．