单选题Late-Night Drinking Coffee lovers beware. Having a quick "pick-me-up" cup of coffee late in the day will play havoc with your sleep. As well as being a stimulant, caffeine interrupts the flow of melatonin, the brain hormone that sends people into a sleep. Melatonin levels normally start to rise about two hours before bedtime. Levels then peak between 2 am and 4 am, before falling again. "It's the neurohormone that controls our sleep and tells our body when to sleep and when to wake," says Maurice Ohayon of the Stanford Sleep Epidemiology Research Center at Stanford University in California. But researchers in Israel have found that caffeinated coffee halves the body's levels of this sleep hormone. Lotan Shilo and a team at the Sapir Medical Center in Tel Aviv University found that six volunteers slept less well after a cup of caffeinated coffee than after drinking the same amount of decal. On average, subjects slept 336 minutes per night after drinking caffeinated coffee, compared with 415 minutes after decal. They also took half an hour to drop off— twice as long as usual—and jigged around in bed twice as much. In the second phase of the experiment, the researchers woke the volunteers every three hours and asked them to give a urine sample. Shilo measured concentrations of a breakdown product of melatonin. The results suggest that melatonin concentrations in caffeine drinkers were half those in decaf drinkers. In a paper accepted for publication in Sleep Medicine, the researchers suggest that caffeine blocks production of the enzyme that drives melatonin production. Because it can take many hours to eliminate caffeine from the body, Ohayon recommends that coffee lovers switch to decaf after lunch.

单选题 Europa's Watery under World Europa, one of Jupiter's 63 known moons, looks bright and icy on the surface. But appearances can be deceiving: Miles within its cracked, frigid shell, Europa probably hides giant pools of liquid water. Where scientists find liquid water, they hope to find life as well. Since we can't go diving into Europa's depths just yet, scientists instead have to investigate the moon's surface for clues to what lies beneath. In a new study, scientists investigated one group of strange ice patterns on Europa and concluded that the formations mark the top of an underground pool that holds as much water as the U. S. Great Lakes. Pictures of Europa, which is slightly smaller than Earth's moon, clearly show a tangled, icy mishmash of lines and cracks known as "chaos terrains." These chaotic places cover more than half of Europa. For more than 10 years, scientists have wondered what causes the formations. The new study suggests that they arise from the mixing of vast underground stores of liquid water with icy material near the surface. For scientists who suspect that Europa also may be hiding life beneath its icy surface, the news about the new lake is exciting. "It would be great if these lakes harbored life, " Britney Schmidt, a planetary scientist who worked on the study, told Science News. "But even if they didn't, they say that Europa is doing something interesting and active right now. " Schmidt, a scientist at the University of Texas at Austin, and her colleagues wanted to know how chaos terrains form. Since they couldn't rocket to Europa to see for themselves, they searched for similar formations here on Earth. They studied collapsed ice shelves in Antarctica and icy caps on volcanoes in Iceland. Those features on Earth formed when liquid water mixed with ice. The scientists now suspect something similar might be happening on Europa: that as water and ice of different temperatures mingle and shift, the surface fractures. This would explain the jumbled ice sculptures. "Fracturing catastrophically disrupts the ice in the same way that it causes ice shelves to collapse on Earth, " Schmidt told Science News. She and her team found that the process could be causing chaos terrains to form quickly on Europa. The new study suggests that on this moon, elements such as oxygen from the surface blend with the deep bodies of water. That mixture may create an environment that supports life.

单选题Volcanic fire and glacial ice are natural enemies. Eruptions at glaciated volcanoes typically destroy ice fields, as they did in 1980 when 70 percent of Mount Saint Helens ice cover was de molished. During long dormant intervals, glaciers gain the upper hand cutting deeply into volcanic cones and eventually reducing them to rubble. Only rarely do these competing forces of heat and cold operate in perfect balance to create phenomenon such as the steam caves at Mount Rainier Park. Located inside Rainier's two ice-filled summit craters, these caves form a labyrinth of tunnels and vaulted chambers about one and one-half miles in total length. Their creation depends on an unusual combination of factors that nature almost never brings together in one place. The cave-making recipe calls for a steady emission of volcanic gas and heat, a heavy annual snowfall at an elevation high enough to keep it from melting during the summer, and a bowl-shaped crater to hold the snow. Snow accumulating yearly in Rainier's summit craters is compacted and compressed into a dense form of ice called firn, a substance midway between ordinary ice and the denser crystalline ice that makes up glaciers. Heat rising from numerous openings (called fumaroles) along the inner crater walls melts out chambers between the rocky walls and the overlying ice pack. Circulating currents of warm air then melt additional opening in the firn ice, eventually connecting the individual chambers and, in the larger of Rainier's two craters, forming a continuous passageway that extends two-thirds of the way around the crater' s interior. To maintain the cave system, the elements of fire under ice must remain in equilibrium, Enough snow must fill the crater each year to replace that melted from below. If too much volcanic heat is discharged, the crater' s ice pack will melt away entirely and the caves will vanish along with the snows of yesteryear. If too little heat is produced, the ice replenished annually by winter snowstorms will expand, pushing against the enclosing crater wails and smothering the present caverns in solid firn ice.

单选题Renewable Energy Sources Today petroleum(石油) 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(矿物燃料). Natural gas reserves could fill 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. Less-polluting renewable energy sources offer a more practical long-term energy solution. "Renewable" refers to the fact that these resources are not used faster than they can be replaced. Hydroelectric(水力发电的)power is now the most common form of renewable energy, supplying around 20% of world electricity. China"s Three Gorges Dam is the largest ever. At five times the size of the U.S."s Hoover Dam, its 26 turbines(涡轮机) 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 use tidal (潮汐的)currents in the open sea opened in Norway. It is designed like windmill(风车), but others take the form of turbines. As prices fall, wind power has become the fastest growing type of electricity generation—quadrupling(翻两番) 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 harmless—they can interfere with radar, alter climate and kill sea birds. Scotland is building Europe"s largest wind farm, which will power 200,000 homes. The U.K."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I enjoy the dish a lot. Can I have the prescription for it?

单选题Some comments are just Uinviting/U trouble.

单选题Computer Mouse The basic computer mouse is an amazingly clever invention with a relatively simple design that allows us to point at things on the computer and it is very productive. Think of all the things you can do with a mouse like selecting text for copying and pasting (涂), drawing, and even scrolling on the page with the newer mice with the wheel. Most of us use the computer mouse daily without stopping to think how it works until it gets dirty and we have to learn how to clean it. We learn to point at things before we learn to speak, so the mouse is a very natural pointing device. Other computer pointing devices include light pens, graphics (图形) tablets and touch screens, but the mouse is still our workhorse. The computer mouse was invented in 1964 by Douglas Englehart of Stanford University. As computer screens became more popular and arrow keys were used to move around a body of text, it became clear that a pointing device that allowed easier motion through the text and even selection of text would be very useful. The introduction of the mouse, with the Apple Lisa computer in 1983, really started the computer public on the road to relying on the mouse for routine (常规) computer tasks. How does the mouse work? We have to start at the bottom, so think upside down for now. It all starts with the mouse ball. As the mouse ball in the bottom of the mouse rolls over the mouse pad, it presses against and turns two shafts (轴). The shafts are connected to wheels with several small holes in them. The wheels have a pair of small electronic light-emitting devices called light-emitting diodes (LED) mounted on either side. One LED sends a light beam to the LED on the other side. As the wheels spin and a hole rotates by, the light beam gets through to the LED on the other side. But a moment later the light beam is blocked until the next hole is in place. The LED detects (发现) a changing pattern of light, converts the pattern into an electronic signal, and sends the signal (发信号) to the computer through wires in a cable that goes out the mouse body. This cable is the tail that helps give the mouse its name. The computer interprets the signal to tell it where to position the cursor on the computer screen. So far we have only discussed the basic computer mouse that most of you probably have or have used. One problem with this design is that the mouse gets dirty as the ball rolls over the surface and picks up dirt. Eventually you have to clean your mouse. The newer optical mice avoid this problem by having no moving parts.

单选题阅读下面的短文，文中有15处空白，每处空白给出了4个选项，请根据短文的内容从4个选项中选择1个最佳答案。 {{B}}A Wonderful Chip{{/B}} It is tiny, only about a quarter of an inch square, and quite flat. Under a microscope, it resembles a stylized Navaho rug or the aerial view of a railroad{{U}} (51) {{/U}}yard. Like the{{U}} (52) {{/U}}of sand on a beach, it is made mostly of silicon,{{U}} (53) {{/U}}oxygen, the most abundant element on the surface of the earth. Yet this inert fleck (小片), still unfamiliar to the{{U}} (54) {{/U}}majority of Americans, has astonishing power. It is cheap to{{U}} (55) {{/U}}produce, fast, infinitely versatile and convenient. The miracle chip represents a quantum(重大的){{U}} (56) {{/U}}in the technology of mankind, a development that{{U}} (57) {{/U}}the past few years has acquired the force and significance associated with the development of hand tools or the discovery of the steam engine. Just as the Industrial Revolution{{U}} (58) {{/U}}an immense{{U}} (59) {{/U}}of tasks from men’s{{U}} (60) {{/U}}and enormously expanded productivity,{{U}} (61) {{/U}}the microcomputer is rapidly assuming huge burdens of drudgery from the human brain and{{U}} (62) {{/U}}expanding the mind’s capacities{{U}} (63) {{/U}}that man has only begun to grasp.{{U}} (64) {{/U}}the chip amazing feats of{{U}} (65) {{/U}}become possible in everything from automobile engines to university laboratories and hospitals, from farms to banks and corporate offices, from outerspace to a baby’s nursery.

单选题We must get to the root of the problem.

单选题Without the greenhouse gases, the earth would

单选题 Male-Female Expectation about Marriage The differences between men and women clarify why they have different expectations about communication in marriage. For women, talk {{U}} {{U}} 1 {{/U}} {{/U}}intimacy. Marriage is an orgy (狂欢) of {{U}} {{U}} 2 {{/U}} {{/U}}: you can tell your feelings and thoughts, and still be loved. Women's greatest fear is being pushed away. But men live in a hierarchical world, {{U}} {{U}} 3 {{/U}} {{/U}}talk maintains independence and statue. They are on {{U}} {{U}} 4 {{/U}} {{/U}}to protect themselves from being put down and pushed around. This {{U}} {{U}} 5 {{/U}} {{/U}}the paradox of the talkative man who said of his silent wife, "She's the talker." In public settings, he feels challenged to {{U}} {{U}} 6 {{/U}} {{/U}}his intelligence and display his understanding. But at home, where he has {{U}} {{U}} 7 {{/U}} {{/U}}to prove and no one to defend against, he is free to remain {{U}} {{U}} 8 {{/U}} {{/U}}. For his wife, being home means she is free from the worry that something she says might {{U}} {{U}} 9 {{/U}} {{/U}}someone, or spark disagreement, or appear to be showing off; at home she is {{U}} {{U}} 10 {{/U}} {{/U}}to talk. The communication {{U}} {{U}} 11 {{/U}} {{/U}}that endanger marriage can't be fixed by mechanical engineering. They require a new conceptual framework about the {{U}} {{U}} 12 {{/U}} {{/U}}of talk in human relationships. Many of the psychological explanations may not be {{U}} {{U}} 13 {{/U}} {{/U}}, because they tend to blame either women (for not being assertive enough) {{U}} {{U}} 14 {{/U}} {{/U}}men (for not being in touch with their feelings). A sociolinguistic approach in {{U}} {{U}} 15 {{/U}} {{/U}}male-female conversation is seen as cross-cultural communication allows us to understand the problem and forge solutions without blaming either party.

单选题There had not been such a severe storm in Trumbull County for a hundred years.

单选题The book provides a concise analysis of the country"s history.

单选题Maria Chapman, abolitionist and close associate of William Lloyed Garrison, wrote many brochures condemning slavery.

单选题{{B}}第三篇{{/B}} {{B}} The Science of the Future{{/B}} Until recently, the "science of the future" was supposed to be electronics and artificial intelligence. Today it seems more and more likely that the next great breakthroughs in technology will be brought through a combination of those two sciences with organic chemistry and genetic engineering. This combination is the science of biotechnology. Organic chemistry enables us to produce marvelous synthetic (合成的) materials. However, it is still difficult to manufacture anything that has the capacity of wool to conserve heat and also to absorb moisture. Nothing that we have been able to produce so far comes anywhere near the combination of strength, lightness and flexibility that we find in the bodies of ordinary insects. Nevertheless, scientists in the laboratory have already succeeded in "growing" a material that has many of the characteristics of human skin. The next step may well be "biotech hearts and eyes" which can replace diseased organs in human beings. These will not be rejected by the body, as is the case with organs from humans. The application of biotechnology to energy production seems even more promising. In 1996 the famous science-fiction writer, Arthur C. Clarke, many of whose previous predictions have come true, said that we may soon be able to develop remarkably cheap and renewable sources of energy. Some of these power sources will be biological. Clarke and others have warned us repeatedly that sooner or later we will have to give up our dependence on non-renewable power sources. Coal, oil and gas are indeed convenient. However, using them also means creating dangerously high levels of pollution. It will be impossible to meet the growing demand for energy without increasing that pollution to catastrophic (灾难性的) levels unless we develop power sources that are both cheaper and cleaner. It is attempting to think that biotechnology or some other "science of the future" can solve our problems. Before we surrender to that temptation we should remember nuclear power. Only a few generations ago it seemed to promise limitless, cheap and safe energy. Today those promises lie buried in a concrete grave in a place called Chernobyl, in the Ukraine. Biotechnology is unlikely, however, to break its promises in quite the same or such a dangerous way.

单选题At midnight, we were {{U}}amused{{/U}} by a knock at the door.

单选题In the United States educational system, intermediate school is the transitional {{U}}phase{{/U}} between the primary grades and high school.

单选题Researchers Discover Why Humans Began Walking Upright Most of us walk and carry items in our hands every day. These are seemingly simple activities that the majority of us don't question. But an international team of researchers, including Dr. Richmond from GW's Columbian College of Arts and Sciences, have discovered that human walking upright, may have originated millions of years ago as an adaptation to carrying scarce, high-quality resources. The team of researchers from the US, England, Japan and Portugal investigated the behavior of modern-day chimpanzees as they competed for food resources, in an effort to understand what ecological settings would lead a large ape—one that resembles the 6 million-year old ancestor we shared in common with living chimpanzees—to walk on two legs. "These chimpanzees provide a model of the ecological conditions under which our earliest ancestors might have begun walking on two legs ", said Dr. Richmond. The research findings suggest that chimpanzees switch to moving on two limbs instead of four in situations where they need to monopolize a resource. Standing on two legs allows them to carry much more at one time because it frees up their hands. Over time, intense bursts of bipedal activity may have led to anatomical changes that in turn became the subject of natural selection where competition for food or other resources was strong. Two studies were conducted by the team in Guinea. The first study was conducted by the team in Kyoto University's "outdoor laboratory" in a natural clearing in Bossou Forest. Researchers allowed the wild chimpanzees access to different combinations of two different types of nut—the oil palm nut, which is naturally widely available, and the coula nut, which is not. The chimpanzees' behavior was monitored in three situations: (a) when only oil palm nuts were available, (b)when a small number of coula nuts were available, and(c) when coula nuts were the majority available resource. When the rare coula nuts were available only in small numbers, the chimpanzees transported more at one time. Similarly, when coula nuts were the majority resource, the chimpanzees ignored the oil palm nuts altogether. The chimpanzees regarded the coula nuts as a more highly-prized resource and competed for them more intensely. In such high-competition settings, the frequency of cases in which the chimpanzees started moving on two legs increased by a factor of four. Not only was it obvious that bipedal movement allowed them to carry more of this precious resource, but also that they were actively trying to move as much as they could in one go by using everything available—even their mouths. The second study, by Kimberley Hockings of Oxford Brookes University, was a 14- month study of Bossou chimpanzees crop-raiding, a situation in which they have to compete for rare and unpredictable resources. Here, 35 percent of the chimpanzees activity involved some sort of bipedal movement, and once again, this behavior appeared to be linked to a clear attempt to carry as much as possible at one time.

单选题He didn"t ignore her intentionally —just didn"t recognize her.

单选题Look After Your Voice Often speakers at a meeting experience dry mouths and ask for a glass of water. You can solve the problem by activating the saliva (唾液) in your mouth. First gently bite the edges of your tongue with your teeth. Or, press your entire tongue to the bottom of your mouth and hold it there until the saliva flow. Or you can imagine that you are slicing (切片) a big juicy lemon and sucking (吮吸) the juice. Before you begin your talk, be kind to your voice. Avoid milk or creamy drinks which coat your throat. Keep your throat wet by drinking a little sweetened warm tea or diluted (稀释的) fruit juice. If you sense, that you are losing your voice, stop talking completely. Save your voice for your speech. You may feel foolish using paper to write notes, but the best thing you can do is to rest your voice. If you need to see a doctor, perhaps you can get some advice from a professional singer. In the meantime, do not even talk in a low voice. What about drinking alcohol to wet your throat? I advice you not to touch alcohol before speaking. The problem with alcohol is that one drink gives you a little confidence. The second drink gives you even more confidence. Finally you will feel all-powerful and you will feel you can do everything, but in fact your brain and your mouth do not work together properly. Save the alcohol until you finish speaking. Perhaps you want to accept the advice, but you may wonder if you can ever change the habits of a lifetime. Of course you can. Goethe, who lived before indoor skating sinks or swimming pools, said, "We learn to skate in the summer and swim in the winter." Take this message to heart and give yourself time to develop your new habits. If you are willing to change, you will soon be able to say that you will never forget these techniques because they became a part of your body.