单选题Black Holes Most scientists agree that black holes exist but are nearly impossible to locate. A black hole in the universe is not a solid object, like a planet, but it is shaped like a sphere (球体). Astronomers (天文学家) think that at the center of a black hole there is a single point in space with infinite (无限的) density (稠密). This single point is called a singularity (奇点). If the singularity theory is correct, it means that when a massive star collapses, all the material in it disappears into the singularity. The center of a black hole would not really be a hole at all, but an infinitely dense point. Anything that crosses the black hole is pulled in by its great gravity. Although black holes do exist, they are difficult to observe. These are the reasons. ·No light or anything else comes out of black holes. As a result, they are invisible to a telescope. ·In astronomical terms, black holes are truly tiny. For example, a black hole formed by the collapse of a giant star would have an event horizon (视界) only 18 miles across. ·The nearest black holes would be dozens of light years away from Earth. One light year is about 6 trillion (万亿) miles. Even the most powerful telescopes could not pick out an object so small at such a great distance. In 1994 the Hubble Space Telescope provided evidence that black holes exist. There are still answers to be found, however, so black holes remain one of the mysteries of the universe.

单选题He kept in Uconstant /U contact with his family while he was in Australia

单选题He endured great pain before he finally expired .

单选题The train stopped abruptly, making us wonder where we were.A. all of a suddenB. fastC. slowlyD. quickly

单选题New Product Will Save Lives Drinking water that looks clean may still contain bugs (虫子), which can cause illness. A small company called Genera Technologies has produced a testing method in three stages, which shows whether water is safe. The new test shows if water needs chemicals added to it, to destroy anything harmful. It was invented by scientist Dr. Adrian Patton, who started Genera five years ago. He and his employees have developed the test together with a British water company. Andy Headland, Genera"s marketing director, recently presented the test at a conference in the USA and forecast good American sales for it. Genera has already sold 11 of its tests at $42,500 a time in the UK and has a further four on order. It expects to sell another 25 tests before the end of March. The company says it is the only test in the UK to be approved by the government. Genera was formed five years ago and until October last year had only five employees. It now employs 14. Mr. Headland believes that the company should make around $19 million by the end of the year in the UK alone.

单选题Her faith upheld her in times of sadness.

单选题Einstein"s Theory of Relativity was so profound that only a few scientists could understand it.

单选题The umbrella was ingeniously devised to fold up into the pocket.

单选题As he is going to work in Holland for two years, he will be parted from his two children.

单选题Is the Tie a Necessity? Ties, or neckties, have been a symbol of politeness and elegance in Britain for centuries. But the casual Prime Minister Tony Blair has problems with them. Reports suggest that even the civil servants may stop wearing ties. So, are the famously formal British really going to abandon the neckties? Maybe. Last week, the UK's Cabinet Secretary Andrew Turnbull openly welcomed a tieless era. He hinted that civil servants would soon be free of the costliest 12 inches of fabric that most men ever buy in their lives. In fact, Blair showed this attitude when he had his first guests to a cocktail party. Many of them were celebrities (知名人士) without ties, which would have been unimaginable even in the recent past. For some more conservative British, the tie is a must for proper appearance. Earlier, Labor leader Jim Callaghan said he would have died rather than have his children seen in public without a tie. For people like Callaghan, the tie was a sign of being complete, of showing respect. Men were supposed to wear a tie when going to church, to work in the office, to a party—almost every social occasion. But today, people have begun to accept a casual style even for formal occasions. The origin of the tie is tricky. It started as something called simply a "band". The term could mean anything around a man's neck. It appeared in finer ways in the 1630s. Frenchmen showed a love of this particular fashion statement. Their neckwear (颈饰) impressed Charles II, the king of England who was exiled (流放) to France at that time. When he returned to England in 1660, he brought this new fashion item along with him. It wasn't, however, until the late 18th century that fancy young men introduced a more colorful, flowing piece of cloth that eventually became known as the tie. Then, clubs, military institutions and schools began to use colored and patterned ties to indicate the wearer's membership in the late 19th century. After that, the tie became a necessary item of clothing for British gentlemen. But now, even gentlemen are getting tired of ties. Anyway, the day feels a bit easier when you wake up without having to decide which tie suits you and your mood.

单选题Image Martian Dust Particles NASA's Phoenix Mars Lander has taken its first-ever picture of a single particle of rusty Martian dust with one of its microscopes. The dust particles of dust were shown at a higher magnification than anything outside of Earth that has been imaged before. The rounded particle measured only about one micrometer, or one millionth of a meter, across. "Taking this image required the highest resolution microscope operated off Earth and a specially designed device to hold the Martian dust," said Tom Pike, a Phoenix science team member from Imperial College London. "We always knew it was going to be technically very challenging to image particles this small." The device that imaged the dust speck is called an atomic force microscope, which maps the shape of particles in three dimensions by scanning them with a sharp tip at the end of a spring. The atomic force microscope can detail the shapes of particles as small as about 100 nanometers. And this won't be the last dust particle that Phoenix will image. "After this first success, we're now working on building up a portrait gallery of the dust on Mars," Pike said. Dust exists everywhere on Mars, coating the surface and giving it its rusty red color. Dust particles also color the Martian sky pink and feed storms that regularly envelope the planet. The ultra-fine dust is the medium that actively links gases in the Martian atmosphere to processes in Martian soil, so it is critically important to understanding Mars' environment, the researchers said. The $420-million Phoenix mission is analyzing the dust and subsurface ice layers of Mars' arctic regions to look for signs of potential past habitability. The particle seen in the atomic force microscope image was part of a sample scooped by the robotic arm from the "Snow White" trench and delivered to Phoenix's microscope station in early July.

单选题It is convenient to purchase things on line.A. readB. buyC. rentD. watch

单选题New Foods and the New World In the last 500 years, nothing about people—not their clothes, ideas, or languages have changed as much as what they eat. The original chocolate drink was made from the seeds of the cocoa tree (可可树) by South American Indians. The Spanish introduced it to the rest of the world during the 1500"s. And although it was very expensive, it quickly became fashionable. In London, shops where chocolate drinks were served became important meeting places. Some still exist today. The potato is also from the New World, around 1600; the Spanish brought it from Peru to Europe, where it soon was widely grown. Ireland became so dependent on it that thousands of Irish people starved when the crop failed during the "Potato Famine (饥荒)" of 1845—1846, and thousands more were forced to leave their homeland and move to America. There are many other foods that have traveled from South America to the Old World. But some others went in the opposite direction. Brazil is now the world"s largest grower of coffee, and coffee is an important crop in Colombia and other South American countries. But it is native to Ethiopia, a country in Africa. It was first made into a drink by Arabs during the 1400"s. According to an Arabic legend, coffee was discovered when a person named Kaldi noticed that his goats were attracted to the red berries on a coffee bush. He tried one and experienced the "wide-awake" feeling that one-third of the world"s population now starts the day with.

单选题 Credit Card Only Works When Spoken To A credit card that will not work unless it hears its owner's voice could become an important weapon in the fight against fraud. The card requires users to give a spoken password that it recognizes using a built-in voice-recognition chip. The idea is to prevent thieves using a stolen card or fraudsters using someone else's credit card details to buy goods online. A model built by engineers at Beepcard in Santa Monica, California, represents the first attempt to pack a microphone, a loud speaker, a battery and a voice-recognition chip into a standard-sized credit card. They are not quite there yet: the card is the length and width of an ordinary credit card, but it is still about three times as thick. Alan Sege, Beepcard's CEO, says the company now plans to use smaller chips to slim it down to normal thickness. The voice card is based on an earlier Beepcard technology designed to prevent fraud in online transactions. This earlier card has no microphone, but has a built-in loudspeaker that it uses to "squawk"(发出叫声) a voice ID signal via a computer's microphone to an online server. By verifying(证实) that the signal matches the card details, the server can establish that the user is not simply keying in a credit card number but actually has the card to hand. The ID code changes each time the card is used in a pre-ordered sequence that only the server knows. This prevents fraudsters recording the beeps, noting the card details and then playing back the audible ID when the key in the details later. But this earlier technology cannot prevent fraudulent use of stolen cards. The new one can. The new voice card also identifies itself by its ID squawk, but it will not do this until it has verified the legitimate user's spoken password. Thieves will be unable to use the card because even if they knew the password they would have to be unable to copy the owner's voice with a high degree of accuracy. The challenge for Beepcard has been to develop voice-recognition and audio circuitry that can be powered by a mini battery embedded in a credit card. To maximize battery life, the electronics are only switched on when the card is being used. Pressing a button on the card's surface prompts it to utter "Say your password" in female voice. If the voice- recognition software proves that the password is authentic, it sends its ID squawk which the server then identifies, allowing the transaction to proceed.

单选题We are sure that he will get over his illness. A．certain B．aware C．happy D．determined

单选题The students had a lot of trouble concentrating on their study because of the noise from the construction outside.A. focusingB. carrying outC. paying forD. continuing with

单选题Arctic Melt Earth's North and South Poles are famous for being cold and icy．Last year，however，the amount of ice in the Arctic Ocean(北冰洋)fell to a record low． Normally，ice builds in Arctic waters around the North Pole each winter and shrinks(缩小)during the summer．But for many years，the amount of ice left by the end of summer has been declining． Since 1979，each decade has seen an 11.4 percent drop in end-of-summer ice cover．Between 1981 and 2000．ice in the Arctic lost 22 percent of its thickness-becoming 1.13 meters thinner． Last summer，Arctic sea ice reached its thinnest levels yet．By the end of summer 2007，the ice had shrunk to cover just 4.2 million square kilometers．That's 38 percent less area than the average cover at that time of year．And it's a very large 23 percent below the previous record low，which was set just 2 years ago．This continuing trend has made scientists concerned． There may be several reasons for the ice melt，says Jinlun Zhang，an oceanographer(海洋学家)at the University of Washington in Seattle．Unusually strong winds blew through the Arctic last summer． The winds pushed much of the ice out of the central Arctic．1eaving a large area of thin ice and open wa ter． Scientists also suspect that fewer clouds cover the Arctic now than in the past．Clearer skies allow more sunlight to reach the ocean．The extra heat warms both the water and the atmosphere．In parts of the Arctic Ocean last year，surface temperatures were 3.5? Celsius warmer than average and 1.5℃ warmer than the previous record high． With both air and water getting warmer，the ice is melting from both above and below．In some parts of the Beaufort Sea，north of Alaska and western Canada，ice that measured 3.3 meters thick at the beginning of the summer measured just 50 cm by season's end． The new measurements suggest that melting is far more severe than scientists have seen by just looking at ice cover from above．Some scientists fear that the Arctic is stuck in a warming trend from which it may never recover．

单选题Something Men Do Not Like to Do Eric Brown hates shopping. "It"s just not enjoyable to me," said the 28-year-old Chicago man who was carrying several shopping bags along the city"s main street, Michigan Avenue. "When I"m out 1 , I basically know what I want to get. I rush in. I buy it. I 2 ." Common wisdom says that guys hate to shop. You can ask generations of men. But people who study shopping say that a number of social, cultural and economic factors are now 3 this "men-hate-to-shop" notion. " 4 social class, ethnicity, age, men say they hate to shop," says Sharon Zukin, a City University of New York sociology professor. "Yet when you ask them deeper questions, it turns out that they 5 to shop. Men generally like to shop for 6 , music and hardware. But if you ask them about the shopping they do for books or music, they"ll say "Well that"s not shopping. That"s 7 ." In other words, what men and women call "buying things" and how they approach that task are 8 . Women will 9 through several 1,000-square-metre stores in search of the perfect party dress. Men will wander through 100 Internet sites in search of the 10 digital camcorder. Women see shopping as a social event. Men see it as a mission or a 11 to be won. "Men are frequently shopping to win," says Mary Ann McGrath, a marketing professor at Loyola University of Chicago. "They want to get the best deal. They want to get the best one. The last one and if they do that it 12 them happy." When women shop, "they"re doing it in a way where they want 13 to be very happy," says McGrath. "They"re kind of shopping for love." In fact, it is in clothing where we see a male-female 14 most clearly. Why, grumble some men, are all male clothes navy, grey, black or brown? But would they wear light green and pink? These days, many guys wear a sort of "uniform", says Paco Underhill, author of "Why We Buy", "It"s been hard for them to understand what it means to be fashion-conscious in a business way. It becomes much, much easier if you 15 your range of choices."

单选题We should not sacrifice environmental protections to foster economic growth.

单选题We should be cautious in crossing a crowded street. A. careful B. intelligent C. quiet D. weary