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.

单选题You should cultivate the habit of reading carefully.

单选题Waving With Light In the Sierra Madre mountain range of west central Mexico, the native Huichol people live much the way their ancestors did without electricity. That's because it's too expensive to string power lines to the remote mountain areas where they live. To help support themselves, the Huichol create beautiful artwork. They sell their art in cities hundreds of miles away from their villages. And without electricity at home or on the road, they can only work during daylight hours. When it gets dark, they must stop whatever they're doing. Now, a team of scientists, designers, and architects are using new technologies to provide the Huichol with light after the sun sets. The scientists' technique involves weaving tiny electronic crystals into fabrics that can be made into clothes, bags, or other items. By collecting the sun's energy during the day, these lightweight fabrics provide bright white light at night. Their inventors have named the fabrics "Portable Lights." Portable Lights have the potential to transform the lives of people without electricity around the world, says project leader Sheila Kennedy. "Our invention," Kennedy says, "came from seeing how we could transform technology we saw every day in the United States and move it into new markets for people who didn't have a lot of money." At the core of Portable Light technology are devices called high-brightness light-emitting diodes, or HB LEDs. These tiny lights appear in digital clocks, televisions, and streetlights. LEDs are completely different from the light bulbs. Most of those glass bulbs belong to a type called incandescent lights. Inside, electricity heats a metal coil to about 2,200 degrees Celsius. At that temperature, bulbs give off light we can see. Ninety percent of energy produced by incandescent lights, however, is heat and invisible. With all that wasted energy, bulbs burn out quickly. They are also easily broken. LEDs, on the other hand, are like tiny pieces of rock made up of molecules that are arranged in a crystal structure. When an electric current passes through an LED, the crystal structure produces light. Unlike incandescent bulbs, they can produce light of various colors. Within an LED, the type of molecules and their particular arrangement determines what color is produced.

单选题Teaching students of threshold level is hard work but the effort is very worthwhile.A. preciousB. rewardingC. worthD. challenging

单选题I remember ______ this used to be quiet village.A. howB. thatC. whereD. what

单选题Freezing to Death for Beauty People in Beijing wear a lot of clothing during winter to fend off (抵御) the cold. In the United States, however, people wear 1 , partly because the car is the primary mode of transportation. Cars take 2 straight to their workplaces, which are heated well. The American diet is full of calories, so their 3 can afford to burn heat more quickly. Fewer layers of clothing give people the opportunity to stay 4 . Lots of Yale girls wear skirts 5 when it"s 10 degrees Centigrade outside. Some of them at least wear boots, tights, and leg-warmers. Some, however, really just go for the look 6 the risk of health. These girls have no pants to protect their 7 , and no socks to protect their feet. A mini skirt and a pair of stilettos (细高跟鞋) are all that they wear. Typically, the ones pursuing fashion are 8 , with little body fat. Just by the nature of their bodies, they are already at a disadvantage compared with normal people in 9 weather. I have always 10 , whenever I pass these girls, how they manage to refrain from shivering and just smile like spring had arrived. And then there are the guys. The girls can be said to 11 health for beauty. But why do guys 12 so little? It is not like, once they take off some layers, they suddenly become better-looking. They are not exactly being fashionable when they 13 wear sporty (花哨的) shorts and shower slippers in the midst of winter. It"s not cute (喜人的). Of course, people have the freedom to look whatever 14 they want. I am just surprised that, given the vast difference between winter and summer temperatures in Connecticut, they can still 15 like they are partying on the beach in the middle of February.

单选题I was impressed by the way he formulated his ideas.

单选题It is now generally assumed that the planets were formed by the accretion of gas and dust in a cosmic cloud.

单选题The economic effects are easy to see. Since 1978, some 43 billion jobs have been lost, largely to forms of technology—either to robotics directly or to computers that are doing what they are supposed to be doing, being labor-saving devices. Today, there is no such thing as a lifetime job; there is no such thing as a career for most people anymore. The jobs that are not done away with are being deskilled, or they are disposable jobs. Even for those jobs that many of you may feel secure with, there are people who are working on what are called "expert systems" to be able to take jobs away from doctors and judges and lawyers. The machine is capable of shredding these jobs as well. But it"s not just the jobs. The economy of jobs and services is trivial compared to the "Nintendo capitalism" that now operates in the world. Four trillion dollars a day is shuffled around the earth as wealth created there. The inevitable result of a Nintendo economy—pulling itself apart, losing jobs, insecure—is the shriveling of the society in which it exists. What we have is an apartheid society, with growing gaps between the rich and poor, and the rich spending a lot of time cocooning themselves from the effects of the poor. A further result of information technology—something that nobody seems to wish to pay much attention to—is the shredding everywhere of the natural world. Forget about the amount of toxins that go into producing these computers, and the resources that go into producing them, such that 40,000 pounds of resources are necessary for a four-pound laptop. That"s trivial compared to the direct effect that computers and the industrial system as a result have on the atmosphere and climate, the pollution of air and water. The development in technology does not always bring human beings goods; there is bad news too. But most people are ignorant of the drawback of the new technology at first. In this century, however, the development in science and technology really aroused people"s attention of the weak points. But the techno-logy has an even darker effect, because it is enabling us to conquer nature. Industrial society is waging a war of the technosphere against the biosphere. That is the Third World War. The bad news is that we are winning that war.

单选题"That"s outrageous !" he protested.

单选题She is incapable of doing the demanding job. A. qualified of B. incompetent with C. good at D. ignorant of

单选题A great deal has been done to remedy the situation. A. maintain B. improve C. assess D. protect

单选题I got a note from Moira {{U}}urging{{/U}} me to get in touch. A. instructing B. pushing C. notifying D. inviting

单选题The council meeting terminated at 2 o'clock. A．began B．continued C．ended D．resumed

单选题Controlling Robots with the Mind Belle, our tiny monkey, was seated in her special chair inside a chamber at our Duke University lab. Her right hand grasped a joystick (操纵杆) as she watched a horizontal series of lights on a display panel. She knew that if a light suddenly shone and she moved the joystick left or right to correspond to its position, she would be sent a drop of fruit juice into her mouth. Belle wore a cap glued to her head. Under it were four plastic connectors, which fed arrays of microwires—each wire finer than the finest sewing thread—into different regions of Belle's motor cortex (脑皮层), the brain tissue that plans movements and sends instructions. Each of the 100 microwires lay beside a single motor neuron (神经元). When a neuron produced an electrical discharge, the adjacent microwire would capture the current and send it up through a small wiring bundle that ran from Belle's cap to a box of electronics on a table next to the booth. The box, in turn, was linked to two computers, one next door and the other half a country away. After months of hard work, we were about to test the idea that we could reliably translate the raw electrical activity in a living being's brain—Belle's mere thoughts—into signals that could direct the actions of a robot. We had assembled a multijointed robot arm in this room, away from Belle's view, which she would control for the first time. As soon as Belle's brain sensed a lit spot on the panel, electronics in the box running two real-time mathematical models would rapidly analyze the tiny action potentials produced by her brain cells. Our lab computer would convert the electrical patterns into instructions that would direct the robot arm. Six hundred miles north, in Cambridge, Mass, a different computer would produce the same actions in another robot arm built by Mandayam A. Srinivasan. If we had done everything correctly, the two robot arms would behave as Belle's arm did, at exactly the same time. Finally the moment came. We randomly switched on lights in front of Belle, and she immediately moved her joystick back and forth to correspond to them. Our robot arm moved similarly to Belle's real arm. So did Srinivasan's. Belle and the robots moved in synchrony (同步), like dancers choreographed (设计舞蹈动作) by the electrical impulses sparking in Belle's mind. In the two years since that day, our labs and several others have advanced neuroscience, computer science and microelectronics to create ways for rats, monkeys and eventually humans to control mechanical and electronic machines purely by "thinking through," or imagining, the motions. Our immediate goal is to help a person who has been unable to move by a neurological (神经的) disorder or spinal cord (脊髓) injury, but whose motor cortex is spared, to operate a wheelchair or a robotic limb.