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The document was {{U}}compiled{{/U}} by the Department of Health. A. written B. printed C. attached D. sent

单选题The leaves have been swept into huge heaps .

单选题She has proved that she can be relied on in a crisis. A. lived on B. depended on C. lived off D. believed in

单选题The workers in that factory manufacture furniture.A. promoteB. paintC. produceD. polish

单选题According to the passage, the science of the future is likely to be

单选题Lower taxes would spur investment and help economic growth.A. attractB. spendC. encourageD. require

单选题There is a need for {{U}}radical{{/U}} changes in education.

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 Urbana-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It's prudent to start any exercise program gradually at first. A．workable B．sensible C．possible D．feasible

单选题 U.S. Blacks Hard-hit by Cancer Death rates for cancer are falling for all Americans, but black Americans are still more likely to die of cancer than whites, the American Cancer Society said Monday. In a special report on cancer and blacks, the organization said blacks are usually diagnosed with cancer later than whites, and they are more likely to die of the disease. This could be because of unequal (不平等的) access to medical care, because blacks are more likely to have other diseases as well, and perhaps because of differences in the biology (生物学) of the cancer itself, the report added. "In general, black Americans have less hope of surviving five years after diagnosis than whites for all cancer sites and all stages of diagnosis," the report said. "In describing cancer statistics for black Americans, this report recognizes that many of the differences associated with race may be caused by unfair social and economic differences and unequal access to medical care." The cancer society said blacks should be encouraged to get check-ups (体格检查) earlier, when cancer is more treatable, and it said more research is needed to see if biological differences play a role. "The new statistics emphasize the continuing importance of wiping out these unfair social differences through public policy and education efforts," the organization said in a statement. But it also noted a drop in cancer death rates. "Cancer death rates in both sexes for all sites combined have dropped greatly among black Americans since 1992, as have incidence rates (发生率)," said the report.

单选题Engineering Ethics Engineering ethics is attracting increasing interest in engineering universities throughout the nation, at Texas A&M University, evidence of this interest in professional ethics culminated in the creation of a new course in engineering ethics, as well as a project funded by the National Science Foundation to develop material for introducing ethical issues into required undergraduate engineering courses. A small group of faculty and administrators actively supported the growing effort at Texas A&M, yet this group must now expand to meet the needs of increasing numbers of students wishing to learn more about the value implications of their actions as professional engineers. The increasing concern for the value dimension of engineering is, at least in part, a result of the attention that the media has given to cases such as the Challenger disaster, the Kansas City Hyatt-Regency Hotel walkways collapse, and the Exxon oil spill. As a response to this concern, a new discipline, engineering ethics, is emerging. This discipline will doubtless take its place alongside such well-established fields as medical ethics, business ethics, and legal ethics. The problem presented by this development is that most engineering professors are not prepared to introduce literature in engineering ethics into their classrooms. They are most comfortable with quantitative concepts and often do not believe they are qualified to lead class discussions on ethics. Many engineering faculty members do not think that they have the time in an already overcrowded syllabus to introduce discussions on professional ethics, or the time in their own schedules to prepare the necessary material. Hopefully, the resources presented herein will be of assistance.

单选题 TV Games Shows One of the most fascinating things about television is the size of the audience. A novel can be on the "best sellers" list with a sale of fewer than 100,000 copies, but a popular TV show might have 70 million TV viewers. TV can make anything or anyone well known overnight. This is the principle behind "quiz" or "game" shows, which put ordinary people on TV to play a game for the prize and money. A quiz show can make anyone a star, and it can give away thousands of dollars just for fun. But all of this money can create problems. For instance, in the 1950s, quiz shows were very popular in the U.S. and almost everyone watched them. Charles Van Doren, an English instructor, became rich and famous after winning money on several shows. He even had a career as a television personality. But one of the losers proved that Charles Van Doren was cheating. It turned out that the show's producers, who were pulling the strings, gave the answers to the most popular contestants beforehand. Why? Because if the audience didn't like the person who won the game, they turned the show off. Based on his story, a movie under the title "Quiz Show" is on 40 years later. Charles Van Doren is no longer involved with TV. But game shows are still here, though they aren't taken as seriously. In fact, some of them try to be as ridiculous as possible. There are shows that send strangers on vacation trips together, or that try to cause newly married couples to fight on TV, or that punish losers by humiliating them. The entertainment now is to see what people will do just to be on TV. People still win money, but the real prize is to be in front of an audience of millions.

单选题Stress Lessen Course Doreen Sykora is now a junior at McGill University. She had a difficult time when she first began college. She said, "I was always well prepared for my examinations. But I would go in to class to take the exam, and I would fall apart. I could not answer the questions correctly--even though I knew the answers! I would just blank out because of nervousness and fear". Histoshi Sakamoto, an anthropology student at Temple University in Tokyo reports similar experiences. These two young students were experiencing something called test anxiety. Because when a student worries and is stressed about a test, his or her mind does not work as well as it usually does. The student cannot write or think clearly because of the severe tension and nervousness. Now there are special university courses to help students. In these courses, advisors and psychologists try to help students by teaching them to manage test anxiety. Such a course helps students learn to live with stress and not fail because of it. First students take a practice test to measure their worry level. If the tests show that their stress level is high, the students can take a short course to manage the fear. These courses teach students how to relax their bodies. They get training to become calm in very tense situations. By controlling their nervousness, they can let their minds work more easily. Learned information then comes out without difficulty on a test. Doreen Sykora saw immediate results after taking such a course. She now has enthusiasm about the relaxation methods. "Mostly, what I do is imagine myself in a very calm place. Then I imagine myself picking up a pencil. I move slowly and carefully. I breathe easily and let all the tension out. With each breath, more worry leaves me. It really works too. My grades have improved greatly! I'm really doing well at McGill now. This relaxation method works not only on examinations, but it has improved the rest of my life as well". For Histoshi in Tokyo, the results were much the same. He is enjoying school a lot more and learning more.

单选题Black Holes What is a black hole? Well, it's difficult to answer this question, since the terms we normally use to describe a scientific phenomenon are inadequate here, Astronomers and scientists think that a black hole is a region of space (not a thing) into which matter has fallen and from which nothing can escape—not even light. So we can't see a black hole. A black hole exerts (施加) a strong gravitational (重力的) pull and yet it has no matter. It is only space—or so we think. How can this happen? The theory is that some stars explode when their density increases to a particular point; they "collapse" and sometimes a supernova (超新星) occurs. The collapse of a star may produce a "White Dwarf (白矮星) "or a "neutron star"—a star whose matter is so dense that it continually shrinks by the force of its own gravity. But if the star is very large this process of shrinking may be so intense that a black hole results. Imagine the earth reduced to the size of a marble, but still having the same mass and a stronger gravitational pull, and you have some idea of the force of a black hole. Any matter near the black hole Is sucked in. It is impossible to say what happens Inside a black hole. Our space and time laws don't seem to apply to objects in the area of a black hole. Einstein's relativity theory is the only one that can explain such phenomena. Einstein claimed that matter and energy are interchangeable, so that there is no "absolute" time and space, There are no constants at all, and measurements of time and space depend on the position of the observer— they are relative. Einstein's theory provided a basis for the idea of black holes before astronomers started to find some evidence for their existence. It is only recently that astronomers have begun specific research into black holes. The most convincing evidence of black holes comes from research into binary (由两部分组成的) star systems. In some binary star systems, astronomers have shown that there is an invisible companion star, a "partner" to the one which we can see in the sky. There is one star, called by its catalogue number HDE 226868, which must have a Partner. This partner star, it seems, has a mass ten or twenty times greater than the sun—yet we can't see it. Matter from HDE 226868 is being dragged towards this companion star. Could this invisible star, which exerts such a great force, be a black hole? Astronomers have evidence of a few other stars too, which might have black holes as companions.

单选题The Texas Opera Theater was established as a {{U}}subsidiary{{/U}} of the Houston Grand Opera in order to give young singers performing their their experience.

单选题{{B}}第二篇{{/B}} Scientists watched closely last spring as a haze of pollution, which had been tracked by satellite as it crossed the Pacific Ocean, settled over a large swath of North America from Calgary, Canada, into Arizona. Now it appears that, for the first time, researchers on both sides of the Pacific took detailed measurements of the same plume, a cloud that contained Gobi desert dust as well as hydrocarbons from industrial pollution. Heather Price, a University of Washington doctoral student in chemistry, found that the amount of light reflected by the particles in the air was more than 550 percent greater than normal for that time of year. The mass of Asian air contained elevated levels of ail pollutants measured. Price said, "but the only thing that came close to being alarming was the level of particulate matter." The haze that settled across the western part of the country was widely reported by the news media, and it was measured as far inland as the ski slopes of Aspen, Colo. Readings on the western side of the Pacific came from the Aerosol Characterization Experiments, a project aimed at understanding how particles in the atmosphere affect Earth's climate. Additional measurements were taken in the same region at the same time under a project sponsored by the National Aeronautics and Space Administration. Knowing the pollution was approaching Washington state, Price loaded sensing equipment aboard a rented Beechcraft on April 14 and flew to Neah Bay on the state's Northwest coast. Taking samples at various levels from 15,000 feet to 20, 000 feet in altitude, she monitored quantities of dust, ozone, carbon monoxide and hydrocarbons. "From my copilot's seat. the dust was thick enough to see with the naked eye." Price said. Now she is trying to correlate her findings with those of the two research teams operating on the other side of the Pacific, where at one point the pollution plume was larger than Japan. The huge size of the cloud showed up clearly in satellite images that gave Price plenty of warning the haze was on its way. "You can see these two blobs coming out of the deserts of Mongolia and growing over Asia, then getting swept out over the ocean and finally setting over North America," she said. She intends to continue measuring air samples off the Washington coast and will be looking for air masses with evidence of pollution originating somewhere other than Asia. "We'd like to see if we can get a signature of pollution coming from Europe because computer models suggest that European sources also can be transported across the Pacific," she said. "However, we expect that sources in Europe will contribute less than Asian sources."

单选题The view from my bedroom window was absolutely {{U}}spectacular{{/U}}. A. general B. traditional C. magnificent D. strong

单选题Computerized firms would rather employ business graduates than computer science graduates because it is easier to train the former into qualified employees.

单选题Many diseases can be cured by orthodox medical treatment.