单选题 The Renewable Energy Sources Today petroleum provides around 40% of the world's energy needs, mostly fuelling automobiles. Coal is still used, mostly in power stations, to cover one-quarter of our energy needs, but it is the least efficient, unhealthiest and most environmentally damaging fossil fuel. Natural gas reserves could plug some of the gap from oil, but reserves of that will not last into the 22nd century either. Most experts predict we will exhaust easily accessible reserves within 50 years. We could fast reach an energy crisis. We need to rapidly develop sustainable solutions to fuel our future. Less-polluting renewable energy sources offer a more practical long-term energy solution. They may benefit the world's poor too. "Renewable" refers to the fact that these resources are not used faster than they can be replaced. Hydroelectric power is now the most common form of renewable energy, supplying around 20% of world electricity. China's Three Gorges Dam, which has just been completed, is the largest ever. At five times the size of the US's Hoover Dam, its 26 turbines will generate the equivalent energy of 18 coal-fired power stations. It will satisfy 3% of China's entire electricity demand. In 2003, the first commercial power station to harness tidal currents in the open sea opened in Norway. It is designed like windmill, but others take the form of turbines. As prices fall, wind power has become the fastest growing type of electricity generation-quadrupling worldwide between 1999 and 2005. Modern wind farms consist of turbines that generate electricity. Though it will be more expensive, there is more than enough wind to provide the world's entire energy needs. Wind farms come in onshore and offshore forms. They can often end up at spots of natural beauty, and are often unpopular with residents. And turbines are not totally benign—they can interfere with radar and leave a significant ecological footprint, altering climate and lilling sea birds. Migrating birds may have more luck avoiding them. Scotland is building Europe's largest wind farm, which wil power 200,000 homes. The UK's goal is to generate one fifth of power from renewable sources, mainly wind, by 2020. But this may cause problems, because wind is unreliable.

单选题______ they can do to help as is not known.A. whatB. whenC. thatD. where

单选题Germs on Banknotes People in different countries use different types of money: yuan in China, pesos in Mexico, pounds in the United Kingdom, (51) in the United States, Australia and New Zealand. They may use different currencies, but these countries, and probably all countries, still have one thing (52) : Germs on the banknotes. Scientists have been studying the germs on money for well over 2, 100 years. (53) the turn of the 20th century, some researchers began to suspect that germs living on money could spread disease. Most studies of germy money have looked at the germs on the currency within one country. In a new study, Frank Vriesekoop and other researchers compared the germ (54) found on bills of different countries. Vriesekoop is a microbiologist at the University of Ballarat in Australia. He led the study, which (55) the germ populations found on money gathered from 10 nations. The scientists studied 1, 280 banknotes (56) ; all came from places where people buy food, like supermarkets, street vendors and cafes, because those businesses often (57) cash. Overall, the Australian dollars hosted the fewest live bacteria—-no more than 10 per square centimeter. Chinese yuan had the most—about 100 per square centimeter. Most of the germs on money probably would not (58) harm. What we call "paper money" usually isn't made (59) paper. The U. S. dollar, for example, is printed on fabric that is mostly cotton Different countries may use different materials to print their money. Some of the currencies studied by Vriesekoop and his team, such as the American dollar, were made from cotton. (60) were made from polymers. The three currencies with (61) numbers of bacteria were all printed on polymers. They included the Australian dollar, the New Zealand dollar and some Mexican pesos. The other currencies were printed on fabric made mostly of cotton. Fewer germs lived on the polymer notes. This connection suggests (62) germs have a harder time staying alive on polymer surfaces. Scientists need to do more studies to understand how germs live on money and (63) or not we need to be concerned. Vriesekoop is now starting a study that will compare the amounts of time bacteria can stay alive on different types of bills. Whatever Vriesekoop finds, the fact (64) : Paper money harbors germs. We should wash our hands after touching it; (65) , you never know where your money's been. Or what's living on it.

单选题Medicine depends on other fields for basic information, particularly some of their specialized branches. A. conventionally B. obviously C. especially D. inevitably

单选题The new theory was corroborated.

单选题The turbulence detector can tell the severity of the turbulence by measuring

单选题During their winter hibernation period, bears doze .

单选题{{B}}第二篇{{/B}} {{B}} External Rewards{{/B}} Psychologists take opposing views of how external rewards, from warm praise to cold cash, affect motivation and creativity. Behaviorists, who study the relation between actions and their consequences, argue that rewards can improve performance at work and school. Cognitive (认识学派的) researchers, who study various aspects of mental life, maintain that rewards often destroy creativity by encouraging dependence on approval and gifts from others. The latter view has gained many supporters, especially among educators. But the careful use of small monetary (金钱的) rewards sparks creativity in grade-school children, suggesting that properly presented inducements (刺激) indeed aid inventiveness, according to a study in the June Journal of Personality and Social Psychology. "If kids know they're working for a reward and can focus on a relatively challenging task, they show the most creativity," says Robert Eisenberger of the University of Delaware in New York. "But it's easy to kill creativity by giving rewards for poor performance or creating too much anticipation for rewards." A teacher who continually draws attention to rewards or who hands out high grades for ordinary achievement ends up with uninspired students, Eisenberger holds. As an example of the latter point, he notes growing efforts at major universities to tighten grading standards and restore failing grades. In earlier grades, the use of socalled token economies, in which students handle challenging problems and receive performancebased points toward valued rewards, shows promise in raising effort and creativity, the Delaware psychologist claims.

单选题Spelling and Writing There is a popular belief among parents that schools are no longer interested in spelling. No school I have taught in has ever ignored spelling or considered it unimportant as a basic skill. There are, however, vastly different ideas about how to teach it, or how much priority(优先) it must be given over general language development and writing ability. The problem is, how to encourage a child to express himself freely and confidently in writing without holding him back with the complexities of spelling? If spelling becomes the only focal point of his teacher"s interest, clearly a bright child will be likely to "play safe". He will tend to write only words within his spelling range, choosing to avoid adventurous language. That"s why teachers often encourage the early use of dictionaries and pay attention to content rather than technical ability. I was once shocked to read on the bottom of a sensitive piece of writing about a personal experience: "This work is terrible! There are far too many spelling errors and your writing is illegible (难以辨认的)." It may have been a sharp criticism of the pupil"s technical abilities in writing, but it was also a sad reflection on the teacher who had omitted to read the essay, which contained some beautiful expressions of the child"s deep feelings. The teacher was not wrong to draw attention to the errors, but if his priorities had centered on the child"s ideas, an expression of his disappointment with the presentation would have given the pupil more motivation to seek improvement.

单选题The project required ten years of {{U}}diligent{{/U}} research．

单选题It is absurd to predict that the sun will not rise tomorrow.

单选题I don't why everything around me is going int confusion.A. considerationB. puzzleC. attractionD. contradiction

单选题I have been trying to give up smoking.A. give offB. put upC. quitD. accept

单选题下面有3篇短文，每篇短文后有5道题。请根据短文内容，为每题确定1个最佳选项。{{B}}第一篇{{/B}} Hair Detectives Scientists have found a way to use hair to figure out where a person is from and where that person has been. The finding could help solve crimes, among other useful applications. Water is central to the new technique. Our bodies break water down into its parts: hydrogen(氢)and oxygen. Atoms (原子) of these two elements end up in our tissues and hair. But not all water is the same. Hydrogen and oxygen atoms can vary in how much they weigh. Different forms of a single element are called isotopes(同位素). And depending on where you live, tap water contains unique proportions of the heavier and lighter isotopes of hydrogen and oxygen. Might hair record these watery quirks(古怪举动；怪僻). That's what James R. Ehleringer, an environmental scientist at the University of Utah in Salt Lake City, wondered. To find out, he and his colleagues collected hair from barbers and hair stylists(发型师)in 65 cities in 18 states across the United States. The researchers assumed that the hair they collected came from people who lived in the area. Even though people drink a lot of bottled water these days, the scientists found that hair overwhelmingly(压倒性地) reflected the concentrations of hydrogen and oxygen isotopes in local tap water. That's probably because people usually cook their food in the local water. What's more, most of the other liquids people drink including milk and soft drinks contain large amounts of water that also come from sources within their region. Scientists already knew how the composition of water varies throughout the country. Ehleringer and colleagues combined that information with their results to predict the composition of hair in people from different regions. One hair sample used in Ehleringer's study came from a man who had recently moved from Beijing, China, to Salt Lake City. As his hair grew, it reflected his change in location. The new technique can't point to exactly where a person is from, because similar types of water appear in different regions that span a broad area. But authorities can now use the information to analyze hair samples from criminals or crime victims and narrow their search for clues(线索).

单选题You must be tired, but try to hang on till all the work"s finished.

单选题Cell Phone Lets Your Secret Out Your cell phone holds secrets about you. Besides the names and (51) that you've programmed into it, traces of your DNA linger (逗留) on the device, according to a new study. DNA is genetic material that (52) in every cell. Like your fingerprint, your DNA is unique to you (53) you have an identical twin. Scientists today routinely analyze DNA in blood, saliva (唾液), or hair left (54) at the scene of a crime. The results often help detectives identify (55) and their victims. Your cell phone can reveal more about you (56) you might think. Meghan J. McFadden, a scientist at McMaster University in Hamilton, Ontario, heard about a crime in which the suspect bled onto a cell phone and later dropped the (57) . This made her wonder whether traces of DNA lingered on cell phones—even when no blood was involved (58) she and colleague Margaret Wallace of the City University of New York analyzed the flip-open phones of 10 volunteers. They used swabs (药签) to collect (59) traces of the users from two parts of the phone: the outside, where the user holds it, and the (60) , which is placed at the user's ear. The scientists scrubbed the phones using a solution made mostly (61) alcohol. The aim of washing was to remove all detectable traces of DNA. The owners got their phones (62) for another week. Then the researchers collected the phones and repeated the swabbing of each phone once more. The scientists discovered DNA that (63) to the phone's speaker on each of the phones. Better samples were collected from the outside of each phone, but those swabs also picked up DNA that belonged to other people who had apparently also handled the phone. (64) , DNA showed up even in swabs that were taken immediately after the phones were scrubbed (擦洗). That suggests that washing won't remove all traces of evidence from a criminal's device. So cell phones can now be added to the (65) of clues that can decide a crime-scene investigation.

单选题 Night of the Living Ants When an ant dies, other ants move the dead insect out of the nest. This behavior is interesting to scientists, who wonder how ants know for sure—and so soon—that another ant is dead. Dong-Hwan Choe, a scientist at the University of California found that Argentine ants have a chemical on the outside of their bodies that signals to other ants, "I'm dead—take me away." But there's a twist to Choe's discovery. These ants are a little bit like zombies (僵尸). Choe says that the living ants—not just the dead ones—have this death chemicals. In other words, while an ant crawls around, perhaps in a picnic or home, it's telling other ants that it's dead. What keeps ants from hauling away the living dead? Choe found that Argentine ants have two additional chemicals on their bodies, and these tell nearby ants something like, "Wait—I'm not dead yet," So Choe's research turned up two sets of chemical signals in ants: one says, "I'm dead," the other set says," I'm not dead yet." Other scientists have tried to figure out how ants know when another ant is dead. If an ant is knocked unconscious, other ants leave it alone until it wakes up. That means ants know that unmoving ants can still be alive. Choe suspects that when an Argentine ant dies, the chemical that says "Wait—I'm not dead yet" quickly goes away. Once that chemical is gone, only the one that says "I'm dead" is left. "It's because the dead ant no longer smells like a living ant that it gets carried to the graveyard (墓地), not because its body releases new unique chemicals after death," said Choe. When other ants detect the "dead" chemical without the "not dead yet" chemical, they haul away the body. This was Choe's hypothesis (假设). To test his hypothesis, Choe and his team put different chemicals on Argentine ant pupae (蛹). When the scientists used the "I'm dead" chemical, other ants quickly hauled the treated pupae away. When the scientists used the "Wait—I'm not dead yet" chemicals, other ants left the treated pupae alone. Choe believes this behavior shows that the "not dead yet" chemicals override (优先于) the "dead" chemical when picked up by adult ants. And that when an ant dies, the "not dead yet" chemicals fade away. Other nearby ants then detect the remaining "dead" chemical and remove the body from the nest.

单选题He was rather vague about the reasons why he never finished school.

单选题Sugar Power for Cell Phones Using enzymes commonly found in living cells, a new type of fuel cell produces small amounts of electricity from sugar. If the technology is able to succeed in mass production, you may some day share your sweet drinks with your cell phone. In fuel cells, chemical reactions generate electrical currents. The process usually relies on precious metals, such as platinum. In living cells, enzymes perform a similar job, breaking down sugars to obtain electrons and produce energy. When researchers previously used enzymes in fuel cells, they had trouble keeping them active, says Shelley D. Minteer of St Louis University. Whereas biological cells continually produce fresh enzymes, there's no mechanism in fuel cells to replace enzymes as they quickly degrade. Minteer and Tamara Klotzbach, also of St Louis University, have now developed polymers that wrap around an enzyme and preserve it in a microscopic pocket. "We tailor these pockets to provide the ideal microenvironment" for the enzyme, Minteer says. The polymers keep the enzyme active for months instead of days. In the new fuel cell, tiny polymer bags of enzyme are embedded in a membrane that coats one of the electrodes. When glucose from a sugary liquid gets into a pocket, the enzyme oxidizes it, releasing electrons and protons. The electrons cross the membrane and enter a wire through which they travel to the other electrode, where they react with oxygen in the atmosphere to produce water. The flow of electrons through the wire constitutes an electrical current that can generate power. So far, the new fuel cells don't produce much power, but the fact that they work at all is exciting, says Paul Kenis, a chemical engineer at the University of Illinois at Urhana-Champaign. "Just getting it to work," Kenis says, "is a major accomplishment." Sugar-eating fuel cells could be an efficient way to make electricity. Sugar is easy to find. And the new fuel cells that run on it are biodegradable, so the technology wouldn't hurt the environment. The scientists are now trying to use different enzymes that will get more power from sugar. They predict that popular products may be using the new technology in as little as 3 years.

单选题What is the Coolest Gas in the Universe? What is the coldest air temperature ever recorded on the Earth? Where was this low temperature recorded? The coldest recorded temperature on Earth was -91℃, which 1 in Antarctica(南极洲) in 1983. We encounter an interesting situation when we discuss temperatures in 2 . Temperatures in Earth orbit(轨道) actually range from about +120℃ to -120℃. The temperature depends upon 3 you are in direct sunlight or in shade. Obviously, -120℃ is colder than our body can 4 endure. The space temperatures just discussed affect only our area of the solar 5 . Obviously, it is hotter closer to the Sun and colder as we travel 6 from the Sun. Scientists estimate temperatures at Pluto are about -210℃. How cold is the lowest estimated temperature in the entire universe? Again, it depends upon your 7 . We are taught it is supposedly 8 to have a temperature below absolute zero, which is -273℃, at which atoms do not move. Two scientists, Cornell and Wieman, have successfully 9 down a gas to a temperature barely above absolute zero. They won a Nobel Prize in Physics in 2001 for their work—not a discovery, in this case. Why is the two scientists" work so important to science? In the 1920s, Satyendra Nath Bose was studying an interesting 10 about special light particles (颗粒) we now call photons (光子). Bose had trouble 11 other scientists to believe his theory, so he contacted Albert Einstein. Einstein"s calculations helped him theorize that atoms 12 behave as Bose thought—but only at very cold temperatures. Scientists have also discovered that ultra-cold (超冷) atoms can help them make the world"s atomic clocks even 13 accurate. These clocks are so accurate today they would only lose one second 14 six million years! Such accuracy will help us travel in space because distance is velocity times time(d=vt). With the long distances involved in space 15 , we need to know time as accurately as possible to get accurate distance.