单选题The Industrial Revolution marked the beginning of an {{U}}epoch{{/U}} of exodus from rural areas to cities.

单选题Man cannot exit without water.

单选题The label on the packet read: "This product contains no Uartificial/U colouring or flavouring."

单选题A task for future scientists is to find out how an animal receives a warning signal.

单选题Customers often defer payment as long as possible. A. make B. demand C. obtain D. postpone

单选题Your dog needs at least 20 minutes of {{U}}vigorous{{/U}} exercise every day. A. energetic B. free C. physical D. regular

单选题The city of New Orleans showed its appreciation for Eleanor McMain's work in social reform by giving her the Times-Picayune award for out-standing service in 1920.

单选题2. Finding Yourself without GPS As more mobile phones tap into the Internet, people increasingly turn to them for location-centric services like getting directions and finding nearby restaurants. While Global Positioning System (GPS) technology provides excellent accuracy, only a fraction of phones have this capability. What's more, GPS coverage is spotty in dense urban environments, and in—phone receivers can be slow and drain a phone's battery. To sidestep this problem, last week Google added a new feature, called My Location, to its Web-based mapping service. My Location collects information from the nearest cell-phone tower to estimate a person's location within a distance of about 1,000 meters. This resolution is obviously not sufficient for driving directions, but it can be fine for searching for a restaurant or a store. "A common use of Google Maps is to search nearby," says Steve Lee, product manager for Google Maps, who likened the approach to searching for something within an urban zip code, but without knowing that code. "In a new city, you might not know the zip code, or even if you know it, it takes time to enter it and then to zoom in and pan around the map." Many phones support software that is able to read the unique identification of a cell-phone tower and the coverage area that surrounds it is usually split into three regions. Lee explains that My Location uses such software to learn which tower is serving the phone—and which coverage area the cell phone is operating in. Google also uses data from cell phones in the area that do have GPS to help estimate the locations of the devices without it. In this way, Google adds geographic information to the cell—phone tower's identifiers that the company stores in a database. As the database grows, says Lee, the service will become more accurate. It will never be as accurate as GPS, but he expects that it could eventually find a person within a couple hundred meters.

单选题Shyness is the cause of much unhappiness for a great many people. Shy people are anxious and selfconscious; that is, they are excessively concerned with their own appearance and actions. Worrisome thoughts are constantly occurring in their minds. What kind of impression am I taking? Do they like me? Do I look stupid? Am I wearing attractive clothes? It is obvious that such uncomfortable feelings must affect people adversely. A person's self-concept is reflected in the way he or she behaves, and the way a person behaves affects other people's reactions. In general, the way people think about themselves has a profound effect on all areas of their lives. Shy people, having low self-esteem, are likely to be passive and easily influenced by others. They need reassurance that they are doing "the right thing". Shy people are very sensitive to criticism; they feel it confirms their inferiority. They also find it difficult to be pleased by compliments because they believe they are unworthy of praise. A shy person may respond to a compliment with a statement like this one, "you are just saying that to make me feel good. I know it's not true." It is clear that, while self-awareness is a healthy quality, overdoing it is harmful. Can shyness be completely eliminated, or at least reduced? Fortunately, people can overcome shyness with determined and patient effort in building self-confidence. Since shyness goes hand in hand with lack of self-esteem, it is important for people to accept their weaknesses as well as their their strengths. For example, most people would like to be "A" student in every subject. It is not fair for them to label themselves inferior because they have difficulty in some areas. People's expectations of themselves must be realistic. Living on the impossible leads to a sense of inadequacy. Each one of us is a unique, worthwhile individual. We are interested in our own personal ways. The better we understand ourselves, the easier it becomes to live up to our full potential. Let's not allow shyness to block our chances for a rich and fullfilling life.

单选题 The Threat to Kiribati The people of Kiribati are afraid that one day in the not-too-distant future, their country will disappear from the face of the earth-literally. Several times this year, the Pacific island nation has been flooded by a sudden high tide. These tides, which swept across the island and destroyed houses, came when there was neither wind nor rain. "This never happened before, "say the older citizens of Kiribati. What is causing these mysterious high tides? The answer may well be global warming. When fuels like oil and coal are being burned, pollutants (污染物)are released; these pollutants trap heat in the earth's atmosphere. Warmer temperatures cause water to expand and also create more water by melting glaciers (冰川)and polar (极地的) ice caps. If the trend continues, scientists say, many countries will suffer. Bangladesh, for example, might lose one-fifth of its land. The coral (珊瑚) island nations of the Pacific, like Kiribati and the Marshall Islands, however, would face an even worse fate—they would be swallowed by the sea. The loss of these coral islands would be everyone's loss. Coral formations are home to more species than any other place on earth. The people of these nations feel frustrated. The sea, on which their economies have always been based, is suddenly threatening their existence. They don't have the money for expensive technological solutions like seawalls. And they have no control over the pollutants, which are being released mainly by activities in large industrialized countries. All they can do is to hope that industrialized countries will take steps to reduce pollution.

单选题Many transmitter towers were built

单选题{{B}}第三篇{{/B}} {{B}}Winged Robot Learns to Fly{{/B}} Learning how to fly took nature millions of years of trial and error --but a winged robot has cracked it in only a few hours, using the same evolutionary principles. Krister Wolff and Peter Nordin of Chalmers University of Technology (CUT) in Gothenburg, Sweden, built a winged robot and set about testing whether it could learn to fly by itself, without any pre-programmed data on what flapping is or how to do it. To begin with, the robot just twitched and jerked erratically. But, gradually, it made movements that gained height. At first, it cheated -- simply standing on its wing tips was one early short cut. After three hours, however, the robot abandoned such methods in favor of a more effective flapping technique, where it rotated its wings through 90 degrees and raised them before twisting them back to the horizontal and pushing down. "This tells us that this kind of evolution is capable of coming up with flying motion," says Peter Bentley, who works on evolutionary computing at University College London. But while the robot had worked out how best to produce lift, it was not about to take off. "There's only so much that evolution can do," Bentley says. "This thing is never going to fly because the motors will never have the strength to do it," he says. The robot had metre-long wings made from balsa wood and covered with a light plastic film. Small motors on the robot let it move its wings forwards or backwards, up or down or twist them in either direction. The team attached the robot to two vertical rods, so it could slide up and down. At the start of a test, the robot was suspended by an elastic band. A movement detector measured how much lift, if any, the robot produced for any given movement. A computer program fed the robot random instructions, at the rate of 20 per second, to test its flapping abilities. Each instruction told the robot either to do nothing or to move the wings slightly in the various directions. Feedback from the movement detector let the program work out which sets of instructions were best at producing lift. The most successful ones were paired up and "offspring" sets of instructions were generated by swapping instructions randomly between successful pairs. These next-generation instructions were then sent to the robot and evaluated before breeding a new generation, and the process was repeated.

单选题She all but fainted when she heard the news.

单选题Take vigorous exercise for several hours a week.

单选题Light Night, Dark Stars Thousands of people around the globe step outside to gaze at their night sky. On a clear night, with no clouds, moonlight, or artificial lights to block the view, people can see more than 14,000 stars in the sky, says Dennis Ward, an astronomer with the University Corporation for Atmospheric Research (UCAR) in Boulder, Colo. But when people are surrounded by city lights, he says, they're lucky to see 150 stars. If you've ever driven toward a big city at night and seen its glow from a great distance, you've witnessed light pollution. It occurs when light from streetlights, office buildings, signs, and other sources streams into space and illuminates the night sky. This haze of light makes many stars invisible to people on Earth. Even at night, big cities like New York glow from light pollution, making stargazing difficult. Dust and particles of pollution from factories and industries worsen the effects of light pollution. "If one city has a lot more light pollution than another," Ward says, "that city will suffer the effects of light pollution on a much greater scale." Hazy skies also make it far more difficult for astronomers to do their jobs. Cities are getting larger. Suburbs are growing in once dark, rural areas. Light from all this new development is increasingly obscuring the faint light given off by distant stars. And if scientists can't locate these objects, they can't learn more about them. Light pollution doesn't only affect star visibility. It can harm wildlife too. It's clear that artificial light can attract animals, making them go off course. There's increasing evidence, for example, that migrating birds use sunsets and sunrises to help find their way, says Sydney Gauthreaux Jr., a scientist at Clemson University in South Carolina "When light occurs at night," he says, "it has a very disruptive influence." Sometimes birds fly into lighted towers, high-rises, and cables from radio and television towers. Experts estimate that millions of birds die this way every year.

单选题Tom"s wife succeeded in persuading him into giving up smoking.

单选题Smoking Can Increase Depressive Symptoms in Teens While some teenagers may use cigarettes to "self-medicate" (自我治疗) against the blues (忧郁), scientists at the University of Toronto and the University of Montreal have found that smoking may actually (51) depressive symptoms in some teens. "This observational study is one of the few to examine the perceived (52) benefits of smoking among teens, "says lead researcher Michael Chaiton, a research associate at the Ontario Tobacco Research Unit of the University of Toronto. " (53) cigarettes may appear to have self-medicating effects or to improve mood, in the long (54) we found that teens who started to smoke reported higher depressive symptoms. " As part of the study, some 662 high school teenagers completed up to 20 questionnaires about their use of cigarettes to (55) mood. Secondary schools were selected to provide a mix of French and English participants, urban and rural schools, and schools (56) in high, moderate and low socioeconomic neighbourhoods. Participants were divided into three (57) : never smokers; smokers who did not use cigarettes to self-medicate, improve mood or physical (58) : smokers who used cigarettes to self-medicate. Depressive symptoms were measured using a scale that asked how often participants felt too tired to do things; had (59) going to sleep or staying asleep; felt unhappy, sad, or depressed; felt hopeless about the future; felt anxious or tense; and worried too much about things. "Smokers who used cigarettes as mood (60) had higher risks of elevated (提升) depressive symptoms (61) teens who had never smoked, " says co-researcher Jennifer O'Loughlin, a professor at the University of Montreal Department of Social and Preventive Medicine. "Our study found that teen smokers who reported emotional benefits from smoking are (62) higher risk of developing depressive symptoms. "The (63) between depression and smoking exists (64) among teens that use cigarettes to feel better. "It's (65) to emphasize that depressive symptom scores were higher among teenagers who reported emotional benefits from smoking after they began to smoke, "says Dr. Chaiton.

单选题Cement was seldom used in buildings of the Middle Ages.

单选题Hersheypark began Uintegrating/U recycling into its public information programs more than five years ago.

单选题I realized to my {{U}}horror{{/U}} that I had forgotten the present.