阅读理解Believe it or not, optical illusion (错觉) can cut highway crashes. Japan is a case in point. It has reduced automobile crashes on some roads by nearly 75 percent using a simple optical illusion. Bent stripes, called chevrons (人字形), painted on the roads make drivers think that they are driving faster than they really are, and thus drivers slow down. Now the American Automobile Association Foundation for Traffic Safety in Washington D.C. is planning to repeat Japan''s success. Starting next year, the foundation will paint chevrons and other patterns of stripes on selected roads around the country to test how well the patterns reduce highway crashes. Excessive speed plays a major role in as much as one fifth of all fatal traffic accidents, according to the foundation. To help reduce those accidents, the foundation will conduct its tests in areas where speed-related hazards are the greatest — curves, exit slopes, traffic circles, and bridges. Some studies suggest that straight, horizontal bars painted across roads can initially cut the average speed of drivers in half. However, traffic often returns to full speed within months as drivers become used to seeing the painted bar. Chevrons, scientists say, not only give drivers the impression that they are driving faster than they really are but also make a lane spear to be narrower. The result is a longer lasting reduction in highway speed and the number of traffic accidents.

阅读理解Living with parents edges out other living arrangements for 18-to 34-year-olds A) Broad demographic (人口的)shifts is marital status, educational attainment and employment have transformed the way young adults in the U

阅读理解Why does the Foundation concentrate its support on basic rather than applied research? Basic research is the very heart of science, and its cumulative product is the capital of scientific progress, a capital that must be constantly increased as the demands upon it rise. The g0al of basic research is understanding, for its own sake. Understanding of the structure of the atom or the nerve cell, the explosion of a spiral nebula(旋涡星云) or the distribution of cosmic dust, the causes of earthquakes and droughts, or of man as a behaving creature and of the social forces that are created whenever two or more human beings come into contact with one another-the scope is staggering, but the commitment to truth is the same. If the commitment were to a particular result, conflicting evidence might be overlooked or, with the best will in the world, simply not appreciated. Moreover, the practical applications of basic research frequently cannot be anticipated. When Roentgen, the physicist, discovered X-rays, he had no idea of their usefulness of medicine. Applied research, undertaken to solve specific practical problems, has an immediate attractiveness because the results can be seen and enjoyed. For practical reasons, the sums spent on applied research in any country always far exceed those for basic research, and the proportions are more unequal in the less developed countries. Leaving aside the funds devoted to research by industry which is naturally far more concerned with applied aspects because these increase profits quickly. The funds the U. S. Government allots to basic research currently amount to about 7 percent of its overall research and development funds. Unless adequate safeguards are provided, applied research invariably tends to drive out basic. Then, as Dr. Waterman has pointed out, "Development will inevitably be undertaken prematurely, career incentives will gravitate strongly toward applied science, and the opportunities for making major scientific discoveries will be lost. Unfortunately, pressures to emphasize new developments, without corresponding emphasize upon pure science.., tend to degrade the quality of the nations technology in the long run, rather than to improve it."

阅读理解Commuting to work in Chicago is no (47)________, for the roads there are even more crowded than in San Francisco. But here is how the city of Chicago is handling the problem. "We don''t have rush hours any more," said Charles M. Mclean, who runs the nation''s busiest road. " We have rush periods, and they keep (48)________ longer and longer. " In Chicago, a (49)________ system has been developed that controls on the city''s seven expressways. Now, one man—a controller can (50)________ the movement of Chicago''s traffic by looking at a set of lights. The system uses electronic sensors that are built into each expressway, half a mile apart. Several times a second, the computer (51)________ information from each sensor and translates it into green, yellow or red lights on a map in the control room. "See that red light near Austin Avenue?" the controller asked a visitor, "That''s a repair truck (52)________ the road, and the traffic has to go around it. " At the Roosevelt "Road entrance to the expressway, the light kept (53)________ from green to red and back to green again. "A lot of trucks get on the expressway there. " the controller explained. "They can''t speed up as fast as cars. " The sensors show in no time where an accident or a stopped car is blocking traffic, and a truck is sent by radio to clear the road. The system has lowered the (54)________ of accidents by percent 18. There are now 1.4 deaths on Chicago''s expressways for each one hundred million miles traveled, while in other parts of the country there are 2. 6. Traffic experts say that the Chicago system is the " coming thing," Systems like Chicago''s are already in use on some expressways in Los Angeles and Houston. "Chicago has (55)________ the lead," says New York City''s transportation director; and he adds, "we are (56)________" WORD BANK A. pleasure B. race C. getting D. receive E. blocking F. computerized G. changing H. percentage I. after J. taken K. pleasant L. accepts M. ratio N. flashing O. behind

阅读理解Six Secrets of High-Energy People There''s an energy crisis in America, and it has nothing to do with fossil fuels. Millions of us get up each morning already weary over the day holds. “I just can''t get started,” People say. But it''s not physical energy that most of us lack. Sure, we could all use extra sleep and a better diet. But in truth, people are healthier today than at any time in history. I can almost guarantee that if you long for more energy, the problem is not with your body. What you''re seeking is not physical energy. It''s emotional energy. Yet, sad to say, life sometimes seems designed to exhaust our supply. We work too hard. We have family obligations. We encounter emergencies and personal crises. No wonder so many of us suffer from emotional fatigue, a kind of utter exhaustion of the spirit. And yet we all know people who are filled with joy, despite the unpleasant circumstances of their lives. Even as a child, I observed people who were poor, or disabled, or ill, but who nonetheless faced life with optimism and vigor. Consider Laura Hillenbrand, who, despite an extremely weak body, wrote the best-seller Seabiscuit. Hillenbrand barely had enough physical energy to drag herself out of be to write. But she was fueled by having a story she wanted to share. It was emotional energy that helped her succeed. Unlike physical energy, which is finite and diminishes with age, emotional energy is unlimited and has nothing to do with genes or upbringing. So how do you get it? You can''t simply tell yourself to be positive. You must take action. Here are six practical strategies that work. 1.Do something new. Very little that''s new occurs in our lives. The impact of this sameness on our emotional energy is gradual, but huge: It''s like a tire with a slow leak. You don''t notice it at first, but eventually you''ll get a flat. It''s up to you to plug the leak — even though there are always a dozen reasons to stay stuck in your dull routines of life. That''s where Maura, 36, a waitress, found herself a year ago. Fortunately, Maura had a lifeline — a group of women friends who meet regularly to discuss their lives. Their lively discussions spurred Maura to make small but nevertheless life-altering changes. She joined a gym in the next town. She changed her look with a short haircut and new black T-shirts. Eventually, Maura gathered the courage to quit her job and start her own business. Here''s a challenge: If it''s something you wouldn''t ordinarily do, do it. Try a dish you''ve never eaten. Listen to music you''d ordinarily tune out. You''ll discover these small things add to your emotional energy. 2.Reclaim life''s meaning. So many of my patients tell me that their lives used to have meaning, but that somewhere along the line things went stale. The first step in solving this meaning shortage is to figure out what you really care about, and then do something about it. A case in point is Ivy, 57, a pioneer in investment banking. "I mistakenly believed that all the money I made would mean something." she says. "But I feel lost, like a 22-year-old wondering what to do with her life." Ivy''s solution? She started a program that shows Wall Streeters how to donate time and money to poor children. In the process, Ivy filled her life with meaning. 3.Put yourself in the fun zone. Most of us grown-ups are seriously fun-deprived. High-energy people have the same day-to-day work as the rest of us, but they manage to find something enjoyable in every situation. A real-estate broker I know keeps herself amused on the job by mentally redecorating the houses she shows to clients. "I love imagining what even the most run-down house could look like with a little tender loving care," she says. "It''s a challenge — and the least desirable properties are usually the most fun." We all define fun differently, of course, but I can guarantee this: If you put just a bit of it into your day, you energy will increase quickly. 4.Bid farewell to guilt and regret. Everyone''s past is filled with regrets that still cause pain. But from an emotional energy point of view, they are dead weights that keep us from moving forward. While they can''t merely be willed away, I do recommend you remind yourself that whatever happened is in the past, and nothing can change that. Holding on to the memory only allows the damage to continue into the present. 5.Make up your mind. Say you''ve been thinking about cutting your hair short. Will it look stylish — or too extreme? You endlessly think it over. Having the decision hanging over your head is a huge energy drain. Every time you can''t decide, you burden yourself with alternatives. Quit thinking that you have to make the right decision; instead, make a choice and don''t look back. 6.Give to get. Emotional energy has a kind of magical quality: the more you give, the more you get back. This is the difference between emotional and physical energy. With the latter, you have to get it to be able to give it. With the former, however, you get it by giving it. Start by asking everyone you meet, “How are you?” as if you really want to know, then listen to the reply. Be the one who hears. Most of us also need to smile more often. If you don''t smile at the person you love first thing in the morning, you''re sucking energy out of your relationship. Finally, help another person — and make the help real, concrete. Give a massage (按摩) to someone you love, or cook her dinner, Then, expand the circle to work. Try asking yourself what you''d do if your goal were to be helpful rather than efficient. After all, if it''s true that what goes around comes around, why not make sure that what''s circulating around you is the good stuff?

阅读理解The medical world is gradually realizing that the quality of the environment in hospitals may play a (47)______ role in the process of (48)______ from illness. As part of a nationwide (49)______ in Britain to bring art out of the galleries and into public places, some of the country''s most talented artists have been called in to transform older hospitals and to soften the hard edges of modern buildings. Of the 2,500 National Health Service hospitals in Britain, almost 100 now have significant collections of (50)______ art in corridors, waiting areas and treatment rooms. These recent initiatives owe a great deal to one artist, Peter Senior, who set up his studio at a Manchester Hospital in northeastern England during the early 1970s. He felt the artist had lost his place in modern society, and that art should be enjoyed by a wider audience. A (51)______ hospital waiting room might have as many as 5,000 visitors each week. What a better place to hold regular exhibitions of art! Senior held the first (52)______ of his own paintings in the outpatients waiting area of the Manchester Royal Hospital in 1975. Believed to be Britain''s first hospital artist, Senior was so much in demand that he was soon joined by a team of six young art school (53)______. The effect is striking. Now in the corridors and waiting rooms the visitor experiences a full view of fresh colors, playful images and restful courtyards. The (54)______ of the environment may reduce the need for expensive drugs when a patient is recovering from an illness. A study has shown that patients who had a (55)______ onto a garden needed half the number of strong painkillers (56)______ with patients who had no view at all or only a brick wall to look at. Word Bank A) contrary B) simply C) view D) significant E) exhibition F) effort G) adopt H) typical I) quality J) culture K) contemporary L) normal M) recovery N) graduates O) compared

阅读理解Passage One According to the majority of Americans, women are every bit as capable of being good political leaders as men

阅读理解Although shark attacks can seem vicious and brutal, it''s important to remember that sharks aren''t evil creatures constantly on the lookout for humans to attack. They are animals obeying their instincts, like all other animals. Sharks are designed to hunt and eat large amounts of meat. A shark''s diet consists of other sea creatures — mainly fish, sea turtles, sea lions, and seals. Humans are not on the menu. In fact, humans don''t provide enough high-fat meat for sharks, which need a lot of energy to power their large, muscular bodies. So why do they attack us? In the majority of recorded attacks, the shark bites the victim, hangs on for a few seconds (possibly dragging the victim through the water or under the surface), and then lets go. The shark is simply mistaking a human for something it usually eats. Once the shark gets a taste, it realizes that this isn''t its usual food, and it lets go. The shark''s confusion is easier to understand once we start to look at things from the shark''s point of view. Many attack victims are surfers. A shark swimming below sees a roughly oval shape with arms and legs dangling off, paddling along. This bears a close resemblance to a sea lion (the main prey of great white sharks) or a sea turtle (a common food for tiger sharks). Attacks have also frequently occurred when humans were spear fishing in ocean waters. Sharks are attracted to the signs given off by dying fish — the smell of blood in the water and the electrical impulses given off as the fish struggles. Sharks detect these signals with their ampullae of Lorenzini, a set of "detectors" under the skin on a shark''s snout (嘴). Once a shark arrives on the scene, it may become agitated and aggressive. There are cases in which sharks seem to attack out of aggression, rather than hunger. Very little is known about shark behavior, but it is believed that some species, including great whites, display dominance behavior over other sharks. This behavior can take the form of "punching" with the snout, or bites that don''t do much damage to the tough skin of a shark. Unfortunately, when a shark makes a dominance display toward a human, these "gentle" bites can still cause horrendous damage. Sometimes, the cause of a shark attack is the shark is responding to human aggression. Nurse sharks, for example, are generally placid fish that lie still along the bottom of the ocean floor. For some reason, this makes some divers think that it''s a good idea to pull their tails. Irritated nurse sharks have taught several divers to keep their hands to themselves. In the next section, we''ll go through a moment-by-moment breakdown of a shark attack.

阅读理解Consumers are being confused and misled by the hodge-podge (大杂烩) of environmental claims made by household products, according to a "green labeling" study (47)______ by Consumers International Friday . Among the report''s more outrageous (令人无法容忍的) findings — a German fertilizer (48)______ itself as "earthworm friendly" a brand of flour said it was "non-polluting" and a British toilet paper claimed to be "environmentally friendlier". The study was written and researched by Britain''s National Consumer Council (NCC) for lobby group Consumer International. It was (49)______by the German and Dutch governments and the European Commission. "While many good and useful claims are being made, it is clear there is a long way to go in (50)______ shoppers are adequately informed about the environmental impact of products they buy," said Consumers International director Anna Fielder. The 10-country study (51)______ product packaging in Britain, Western Europe, Scandinavia and the United States. It found that products sold in Germany and the United Kingdom made the most environmental claims on (52)______ . The report focused on claims made by (53)______ products, such as detergent (洗涤剂) insect sprays and by some garden products. It did not test the claims, but (54)______ them to labeling guidelines set by the International Standards Organization (ISO) in September, 1999. Researchers documented claims of environmental friendliness made by about 2,000 products and found many too vague or too misleading to meet ISO standards. The ISO labeling standards (55)______ vague or misleading claims on product packaging, because terms such as "environmentally friendly" and "non-polluting" cannot be (56)______ . " What we are now pushing for is to have multinational corporations meet the standards set by the ISO," said Page. Word Bank A) verified I) described B) assured J) funded C) ensuring K) surveyed D) environmental L) balance E) specific M) average F) comparing N) support G) compared O) ban H) published

阅读理解Jan. 6 issue--The weather outside was icy, but inside, 250 journalists were gathered in a Manhattan office complex to see the latest schemes for rebuilding the World Trade Center site. Last week was the first hope that something good for the city could emerge from September 11. A year ago New York Governor George Pataki established the Lower Manhattan Development Corporation to be responsible for the rebuilding. The agency has bungled the effort more than once. Last summer the public gave its first set of plans a Bronx cheer (嘘声), urging the LMDC to hold an international competition for new designs. From more than 400 applicants, it chose six teams of designers (a seventh firm, LMDC consultants Peterson/Littenberg, was added later). The most futuristic aspects of the schemes are in the skyline--several call for the tallest buildings in the world. British architect Norman Foster says his firm''s two towers "kiss and touch and become one"; Team United offers a cluster of towers that lean into each other; the team of Richard Meier, Peter Eisenman, Charles Gwathmey and Steven Holl proposes five high rises, joined by horizontal connectors. All these links were inspired by the need to give multiple exit options. But more critical--and more likely to become reality than any of these specific towers--is how the various schemes treat the street level and underground. Most, by putting rentable office space up high, were generous with parks and cultural facilities. The teams were told to create sites for a memorial--and several couldn''t resist designing one. Libeskind was struck by the "great slurry (泥浆) wails" 70 feet down that survived the attack, a dike (堤防) against landfill and an engineering miracle of its time--and he leaves them as a memorial, adding a waterfall and a museum. Foster suggests two memorials in the areas of the Twin Towers'' foot prints, one for families of victims, the other for the public.

阅读理解The beat generation mainly referred to the youth who were born and brought up around the Second World War. They showed their disdain (蔑视，轻视) for almost everything traditional, such as government authority, respect for parents, one''s duty, moral standards, and traditional customs. They developed a kind of absolute individualism and liberty. They preferred long hair, mini-dresses or close-fitting clothes to show off the figure. They advocated freedom of sex and cohabitation (同居). Their influence could be seen from the fact that about one third of the American couples living together were not married by law. And the divorce rate was very high. The endless U. S. wars abroad and sharp class struggle at home caused many American youths to develop a kind of cynicism. They doubted the existing social system, possibility of harmonious human relations, and the long-honored standard for correct behavior. They felt society overlooked their needs. Therefore, they refused to do any duty that was required of them by society. They declared "Don''t believe anyone over thirty. "All this came from the sick society. It''s wrong to imagine they all fought against capitalism in support of revolutionary things. Some of their ideas were even more decadent (颓废的) and impractical. It was an abnormal phenomenon in an abnormal society.

阅读理解Passage One Some radio singals were heard in 1967

阅读理解What is Ales Pang's recommendation for Internet users?

阅读理解The first baby in Britain to survive a heart transplant celebrated her 18th birthday yesterday. Kaylee Davidson was five months old when she received a new heart during a (47) operation at the Freeman Hospital, Newcastle upon Tyne, in 1987. Now fit and healthy, she studies performing arts at a college in Sunderland and is in training to (48) Britain at the World Transplant Games in Canada this summer. Miss Davidson, who admitted that she was "looking forward to my first (49) drink", will be the guest of honor (嘉宾) tomorrow at a charity ball which is being held to mark her coming of age. "I am living (50) that people can make a difference by becoming an organ donor," she said. "I was only five months old when I had my transplant, just a tiny baby. I wasn''t given much chance, but the doctors were (51) and I was lucky enough to grow stronger and stronger." Her mother, Carol Davidson, 37 yesterday (52) that for the first few weeks of her daughter''s life all had seemed (53) , until one evening, when she suddenly had breathing difficulties. A GP (普通全科医师) suggested that Kaylee was suffering from a (54) cold, but within 24 hours her lips turned blue. She was admitted to hospital and placed on a life-support machine. Her mother, a school inspector, said: "My baby'' s heart was destroyed and the doctors said she would (55) without a transplant." Till then, there had been no successful heart transplants on babies in Europe. The two (56) in Britain had both failed. WORD BANK A) legal I) severe B) attempts J) recalled C) amazing K) breakthroughs D) condemn L) depart E) pioneering M) proof F) reminded N) spark G) normal O) represent H) complicated

阅读理解For some educators, there is nothing wrong with fun and games. A group called the Education Arcade recently held a conference in Los Angeles to discuss the future of educational games. The Education Arcade brings together international game designers, publishers, teachers and policymakers. They say they want to lead change in the way the world learns through computer and video games. The conference was part of E-three, the Electronic Entertainment Exposition. This is a yearly trade show where companies show off new games and educational products. The Education Arcade started at the Massachusetts Institute of Technology, near Boston. Professors worked with the Microsoft company to create what they called the Games-to-Teach Project. The group began to explore ways to use technology in teaching and learning. They worked with game designers to develop ideas about how mathematics and science could mix with game playing. The Education Arcade is the research part of this Games-to-Teach Project. The group recently announced that a "Games for Learning" statement will be placed on some products. This should begin to appear in American stores in about six months. The goal is to help people find games that are fun but will also teach. The Education Arcade says it also wants to get businesses to produce more games that teach. The Entertainment Software Association says fifty percent of all Americans age six and older play computer and video games. Sales of such games in the United States grew eight percent last year, to seven-thousand-million dollars. The industry group says the average age of a game player is twenty-nine years old. And it says thirty-nine percent are women. Experts say developing a successful computer game can take millions of dollars and years of work. They say many companies are not willing to invest that much money and time in educational games when other kinds sell better. Still, companies have been creating systems like hand-held educational devices made by LeapFrog. And new educational role-playing games are being developed. M.I.T. and the Colonial Williamsburg Foundation in Virginia are developing a game called "Revolution." Players will get to experience the American Revolution online.

阅读理解It seems the art of survival—or continual positive projection—in the world of pop music these days, depends very much on change. If artists fail to recreate their image—chameleon(变色龙)-like, over and over again—they risk facing accusations of dullness; that they are not fashionable. This phenomenon is especially prevalent(普遍的) in the female ranks. It is not sufficient for an artist to be beautiful and sexy. These characteristics too must be changed often, and remodelled to avoid being bogged down(陷入困境) by a stereotype(老一套). Two examples of the rock "n" roll art of move and change are Cher and Madonna, the latter a brilliant illustration of the trend. Her latest disc, "Something to Remember", displays how she has so effectively been able to stay at the top without diminishing credibility in her particular field. (For these purposes, we will forget her unworthy flirtation with sex, that horrible book and her swear-word-ridden, cigar-chewing appearance on the David Letterman Show. ) This collection demonstrates how she has moderate her image at relevant times to give contrast and definition to her career. But it offers more than simply a study in rock fashion history. There is also a solid collection of quality music. It opens with the newish "I Want You with Massive Attack", a faintly morose and teary plea and quickly moves back in time to her earlier moments: "Crazy for You", "This Used To Be My Playground" and "You''ll See". There is also a nice version of "Love Don''t Live Here Anymore". So this is more than an exploitative offering. However, Cher''s latest package, ''It''s a Man''s World'', cannot be reviewed proudly. In her past — the most memorable moment for this reviewer being her visit to a US warship amid cheering sailors for "If I Could Turn Back Time" — she has competed admirably. And she has demonstrated the classic features of the change syndrome(综合症). But this is a tired and dull Cher, Perhaps attempting to moderate her sexy and boy-crazy image in this session but failing.

阅读理解A is for always getting to work on time. B is for being extremely busy. C is for the conscientious (勤勤恳恳的) way you do your job. You may be all these things at the office, and more. But when it comes to getting ahead, experts say, the ABCs of business should include a P, for politics, as in office politics. Dale Carnegie suggested as much more than 50 years ago: Hard work alone doesn''t ensure career advancement. You have to be able to sell yourself and your ideas, both publicly and behind the scenes. Yet, despite the obvious rewards of engaging in office politics -- a better job, a raise, praise -- many people are still unable -- or unwilling -- to "play the game." "People assume that office politics involves some manipulative (工于心计的) behavior," says Deborah Comer, an assistant professor of management at Hofstra University. " But politics derives from the word "polite". It can mean lobbying and forming associations. It can mean being kind and helpful, or even trying to please your superior, and then expecting something in return." In fact, today, experts define office politics as proper behavior used to pursue one''s own self-interest in the workplace. In many cases, this involves some form of socializing within the office environment -- not just in large companies, but in small workplaces as well. "The first thing people are usually judged on is their ability to perform well on a consistent basis," says Neil P. Lewis, a management psychologist. "But if two or three candidates are up for a promotion, each of whom has reasonably similar ability, a manager is going to promote the person he or she likes best. It''s simple human nature." Yet, psychologists say, many employees and employers have trouble with the concept of politics in the office. Some people, they say, have an idealistic vision of work and what it takes to succeed. Still others associate politics with flattery (奉承), fearful that, if they speak up for themselves, they may appear to be flattering their boss for favors. Experts suggest altering this negative picture by recognizing the need for some self-promotion.

阅读理解Why are Millennials over-confident about themselves?

阅读理解Passage oneQuestions 46 to 50 are based on the following passage

阅读理解A Roof over our Heads Man has three basic needs: food, clothing, and shelter. If a man lives in a warm climate, clothing is not absolutely necessary. However, man cannot live without food, and, he has little chance of survival without shelter. Mankind needs shelter to protect him from the weather, wild animals, insects, and his enemies. Long before man learned how to build houses, he looked for natural shelters, as the animals did. He found that he could protect himself by climbing up into trees or by crouching under the over-hanging edges of cliffs, or by crawling into caves. The first shelters or homes actually built by man were very simple. For his building materials, he used what he could find easily around him: rocks, tree branches, dried grasses, animal skins. It was a long time, however, before man began to build permanent shelters because, until man learned to farm, he lived by hunting. And, in order to follow game, he had to be able to move from one hunting ground to another. Thus, the first man-made shelters were those that could be easily transported. The first permanent shelters were probably built twenty to forty thousand years ago by fish eating people who lived in one place as long as the fish supply lasted. Fish-eaters could stay in one place for several years. However, once man learned to farm, he could live longer in one place. Thus, he was able to build a permanent home. Once again, he built his home with the materials he found at hand. In Egypt, for example, wood was scarce, so most houses were built of bricks made of dried mud, with a roof supported by palm tree trunks. When the Norsemen came from Scandinavia to northern Europe, they found many forests, so they built homes with a framework of heavy tree trunks and they filled the space between the trunks with clay. The Eskimos, on the other hand, lived in a land where there was little or no wood. They learned to adapt their homes perfectly to their surroundings. In the winter time, when everything was covered with snow and ice, the Eskimos built their homes with blocks of ice. When the warm weather came and melted the ice, the Eskimos lived in a tent made of animal skins. The weather is man'' s worst natural enemy. He has to protect himself from extremes of heat and cold and from storms, wind and rain. Where the weather is hot and dry, the house is generally made of clay brick. The windows are small and high up, so that the heat stays outside. There is often a fiat roof, where people can find a cool place to sleep. In hot, humid areas, on the other hand, people need to be protected from the rain, as well as the heat. In such places, houses are built with wide, overhanging roofs, balconies or verandas (走廊). Where there are torrential rains, houses are either built on piles to keep them off the ground, or they have steep thatched (茅草屋顶的) roofs to drain off the rain. People living in the Congo River region have found that steep, heavily-thatched roofs drain off the jungle rains more quickly. Other people in Africa have found that a roof of broad leaves sheds rain quickly. In Borneo, houses are built on high posts to protect people from dampness. And there are tribes in Malaya who build their homes in the forked branches of trees, and climb up to their houses on bamboo ladders. In northern countries, people build houses to protect themselves from cold and snow. Their houses are built of sturdy materials, and the roofs are steep, so that the snow will slide off. There are also overhanging eaves (屋檐) to keep the snow from piling up next to the house. And, in northern Siberia, where snowfall is extremely heavy, the roofs even have a funnel-shaped (漏斗状的) platform to protect the chimneys from drifting snow. Protection from danger has also influenced the type of house man builds. When. enemies threatened him, man made his house as inaccessible as possible. The tree-dwellers of the Philippines protect themselves by living high above the ground. When danger threatens, they remove the ladders leading to their homes. The cliff dwellers of the American Southwest built their homes high up on the sides of cliffs, where access was very difficult. Nomad (游牧的) tribes must move from place to place, taking care of flocks of sheep that are always in need of fresh grass. Their houses must be simple and easy to transport. The nom ads of central Asia,-have developed a house made of a framework of poles covered with felt (毛毡). The house is round because the framework is curved. The poles are fastened together at the top with a wooden ring, and there is a hole at the top to let the smoke out. In Europe there are very few wooden houses being built today. This is partly because wood is no longer as plentiful as it once was, and partly because wooden houses are quite inflammable (易燃的). On the other hand, there are many wooden houses in America. This is because the first settlers wanted to build houses quickly and inexpensively. Since the country was covered in many places with forests, some trees had to be cut down to make room for houses. Houses in many cities used to be made of wood. However, since the houses were very close together, fire could easily spread from one house to another. There were disastrous fires in some cities, such as the great fire of London in 1666. When the burned-out cities were rebuilt, wood was still used for the frames and the roofs, but stones or bricks were used for walls. There are so many people living in some cities that it is often very difficult to find a place to live, and if one does find a place it is often too small. And many of the houses are too old and uncomfortable. Just as in prehistoric times, finding a good place to live continues to be one of man'' s most urgent problems.