单选题If Johnny can't write, one of the reasons may be a conditioning based on speed rather than respect for the creative process. Speed is neither a valid test nor a proper preparation for competence in writing. It makes for gloominess, glibness, disorganization. It takes the beauty out of the language. It rules out respect for the reflective thought that should precede expression. It runs counter to the word-by-word and line-by-line reworking that enables a piece to be finely knit. This is not to minimize the value of genuine facility. With years of practice, a man may be able to put down words swiftly and expertly. But it is the same kind of swiftness that enables a cellist, after having invested years of efforts, to negotiate an intricate passage from Haydn. Speed writing is for stenographers and court reporters, not for anyone who wants to use language with precision and distinction. Thomas Mann was not ashamed to admit that he would often take a full day to write 500 words, and another day to edit them, out of respect for the most difficult art in the world. Flaubert would ponder a paragraph for hours. Did it say what he wanted it to say not approximately but exactly? Did the words turn into one another with proper rhythm and grace? Were they artistically and securely fitted together? Were they briskly alive, or were they full of fuzz and ragged edges? Were they likely to make things happen inside the mind of the reader, igniting the imagination and touching off all sorts of new anticipations? These questions are relevant not only for the established novelist but for anyone who attaches value to words as a medium of expression and communication. E.B. White, whose respect for the environment of good writing is expressed by no word-artist of our times, would rather have his fingers cut off than to be guilty of handling words lightly. No sculptor chipping away at a granite block in order to produce a delicate curve or feature has labored more painstakingly than White in fashioning a short paragraph. Obviously, we can't expect our schools to make every Johnny into a White or a Flaubert or a Mann, but it is not unreasonable to expect more of them to provide the conditions that promote clear, careful, competent expression. Certainly the cumulative effort of the school experience should not be undone in later years.

单选题Survey results indicate that smoking and alcohol and marijuana use increased among residents of Manhattan during the 5～8 weeks after the terrorist attacks on the World Trade Center winch took place on September 11, 2001. Almost one-third of the nearly 1,000 persons interviewed reported an increased use of alcohol, marijuana, or cigarettes following the September 11th attacks. The largest increase was in alcohol use. About one-fourth of the respondents said they were drinking more alcohol in the weeks after September 11; about 10% reported an increase in smoking, and 3.2% said they had increased their use of marijuana. The investigators found survey participants by randomly dialing New York City phone numbers and screened potential respondents for Manhattan residents living in areas close to the World Trade Center. Interviews were conducted with 988 individuals between October 16 and November 15, 2001. Participants were asked about their cigarette smoking, alcohol drinking, and marijuana use habits before and after September 11. During the week prior to September 11, 2001, 22. 6% of the participants reported smoking cigarettes, 59. 1% drinking alcohol, and 4.4% using marijuana. After September 11th, 23.4% reported smoking cigarettes, 64. 4% drinking alcohol, and 5.7% smoking marijuana. Among those who smoked, almost 10% reported smoking at least an extra pack of cigarettes a week and among those who drank alcohol, more than 20% reported imbibing at least one extra drink a day. The researchers found that people who reported an increase in substance abuse were more likely to suffer from post traumatic stress disorder (PTSD) and from depression. People who reported an increase in cigarette smoking or marijuana use were also more likely to have both PTSD and depression, while those who reported an increase in alcohol use were more likely to have depression only. Persons who were living closer to the World Trade Center were more likely to increase their cigarette smoking, but other factors such as being displaced from home, losing possessions during the attacks, or being involved in the rescue efforts were not consistently associated with increased substance use. Symptoms of panic attack were associated with an increase in the use of all substances. Increase in substance abuse did not differ significantly between men and women or among racial or ethnic groups. Demographic factors such as age, marital status, and income seemed to play a more critical role in determining if the events of September 11th led to an increase in substance use.

单选题Stockbrokers are agents who buy and sell stocks, shares and other securities for their clients. They are paid commission. Jobbers, on the other hand, buy and sell securities in large quantities. They are the wholesalers. The jobbers are always to be found in the same spot in the London Stock Exchange. They congregate according to the type of security they specialize in. So you can find all the jobbers dealing with rubber shares in one place, those interested in shipping another, those concerned with mining in another, and so on. Jobbers make a profit like any other dealer. They usually quote two prices; they are prepared to buy any reasonable quantity of that share at the lower price, and to sell at the higher price. These prices vary, of course, from day to day and even hour to hour, according to the demand. Perhaps a broke wants to sell five hundred shares in XYZ Pharmaceuticals for a client. He looks for the jobbers who deal in pharmaceutical shares. He asks the price of XYZ Pharmaceuticals, without saying whether he wishes to buy or sell. The jobber quotes him two prices—perhaps 75/79. This means that he will buy quantities of that share at 75 pence each, and sell them at 79 pence each. The broker then goes on to other jobbers and asks them the same question. Eventually he chooses the best offer. The two men make a verbal agreement (nothing is written at this stage) and from that moment the broker's client is the owner of those shares. When he goes back to his office, the broker has to write out a "contract note", which he sends to his client. This records the price, his commission, the tax on the transaction, and so on. For payment, both the buyer and the seller must sign transfer forms; these are sent to XYZ Pharmaceuticals for registration. Later, the buyer gets a certificate of the shares. The deal is now complete. The London Stock Exchange has always been famous as a place for men. only, and women used to be strictly forbidden to enter. But the world is changing day by day, and even the Stock Exchange, which seemed to be a man's castle, is gradually opening its doors to the other sex. On 16th November, 1971, a great decision was taken. The Stock Exchange Council (the body of men that administers the Stock Exchange) decided that Women should be allowed on to the new trading floor when it opened in 1973. But the "castle" had not been completely conquered. The first girls to work in "The House" were not brokers or jobbers. They were neither allowed to become partners in stockbroking firms, nor to be authorized dealers in stocks and shares. They were simply junior clerks and telephone operators. Women have been trying to get into the Stock Exchange for many years. Several votes have been taken in "The House" to see whether the members would be willing to allow women to become members, but the answer has always been "NO". There have been three refusals of this kind since 1967. Now women are admitted, although in a very junior capacity. Two firms of jobbers made an application to the Stock Exchange Council to be allowed to employ girl clerks. Permission was finally given. A member of the Stock Exchange explained, after this news had been given, "The new floor is going to be different from the old one. All the jobbers will have their own stands, with space for a telephone and typewriters. Therefore there will have to be typists and telephone operators. So women must be allowed in." This decision did not mean a very great victory in the war for equal rights for women. However, it was a step in the right direction. The Chairman of the Stock Exchange said, "I think that the opening of the new building will eventually lead to women being allowed to have full membership of the Stock Exchange. It is only a matter of time; it must happen".

单选题Questions 14 to 16 are based on the following talk. You now have 15 seconds to read Questions 14 to 16.

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单选题 Text 3 Most growing plants contain much more water than all other materials combined. C.R. Barnes has suggested that it is as proper to term the plant a water structure as to call a house composed mainly of brick a brick building. Certain it is that all essential processes of plant growth and development occur in water. The mineral elements from the soil that are usable by the plant must be dissolved in the soil solution before they can be taken into the root. They are carried to all parts of the growing plant and are built into essential plant materials while in a dissolved state. The carbon dioxide (CO2) from the air may enter the leaf as a gas but is dissolved in water in the leaf before it is combined with a part of the water to form simple sugars the base material from which the plant body is mainly built. Actively growing plant parts are generally 75 to 90 percent water. Structural parts of plants, such as woody stems no longer actively growing may have much less water than growing tissues. The actual amount of water in the plant at any one time, however, is lonly a very small part of what passes through it during its development. The processes of photosynthesis, by which carbon dioxide and water are combined — in the presence of chlorophyll and with energy derived from light — to form sugars, require that carbon dioxide from the air enter the plant. This occurs mainly in the leaves. The leaf surface is not solid but contains great numbers of minute openings, through which the carbon dioxide enters. The same structure that permits the one gas to enter the leaf, however, permits another gas — water vapor — to be lost from it. Since carbon dioxide is present in the air only in trace quantities (3 to 4 parts in 10,000 parts of air) and water vapor is near saturation in the air spaces within the leaf (at 80, saturated air would contain about 186 parts of water vapor in 10,000 parts of air), the total amount of water vapor lost is many times the carbon dioxide intake. Actually, because of wind and other factors, the loss of water in proportion to carbon dioxide intake may be even greater than the relative concentrations of the two gases. Also, not all of the carbon dioxide that enters the leaf is synthesized into carbonhy drates.

单选题----- which _______，bread or rice？ ----- ________will do.

单选题In the last paragraph, what does the author probably imply by "something terrible"?

单选题Questions 4～6 are based on the following passage; listen and choose the best answer.

单选题 {{B}} Questions 14 to 17 are based on a talk by a tourist agent on the Canyonland in Utah. You now have 20 seconds to read Questions 14 to 17.{{/B}}

单选题{{B}}Text 2{{/B}} At 18, Ashanthi DeSilva of suburban Cleveland is a living symbol of one of the great intellectual achievements of the 20th century. Born with an extremely rare and usually fatal disorder that left her without a functioning immune system (the "bubble-boy disease", named after an earlier victim who was kept alive for years in a sterile plastic tent), she was treated beginning in 1990 with a revolutionary new therapy that sought to correct the defect at its very source, in the genes of her white blood cells. It worked. Although her last gene-therapy treatment was in 1992, she is completely healthy with normal immune function, according to one of the doctors who treated her, W. French Anderson of the University of Southern California. Researchers have long dreamed of treating diseases from hemophilia to cancer by replacing mutant genes with normal ones. And the dreaming may continue for decades more. "There will be a gene-based treatment for essentially every disease," Anderson says, "within 50 years. " It's not entirely clear why medicine has been so slow to build on Anderson' s early success. The National Institutes of Health budget office estimates it will spend $ 432 million on gene-therapy research in 2005, and there is no shortage of promising leads. The therapeutic genes are usually delivered through viruses that don' t cause human disease. "The virus is sort of like a Trojan horse," says Ronald Crystal of New York Presbyterian/Weill Cornell Medical College. "The cargo is the gene. " At the University of Pennsylvania's Abramson Cancer Center, immunologist Carl June recently treated HIV pa tients with a gene intended to help their cells resist the infection. At Cornell University, researchers are pursuing gene-based therapies for Parkinson's disease and a rare hereditary disorder that destroys children' s brain cells. At Stanford University and the Children' s Hospital of Philadelphia, researchers are trying to figure out how to help patients with hemophilia who today must inject themselves with expensive clotting drugs for life. Animal experiments have shown great promise. But somehow, things get lost in the translation from laboratory to patient. In human trials of the hemophilia treatment, patients show a response at first, but it fades over time. And the field has still not recovered from the setback it suffered in 1999, when Jesse Gelsinger, an 18-year-old with a rare metabolic disorder, died after receiving an experimental gene therapy at the University of Pennsylvania. Some experts worry that the field will be tarnished further if the next people to benefit are not patients but athletes seeking an edge. This summer, researchers at the Salk Institute in San Diego said they had created a "marathon mouse" by implanting a gene that enhances running ability; already, officials at the World Anti-Doping Agency are preparing to test athletes for signs of "gene doping". But the principle is the same, whether you're trying to help a healthy runner run faster or allow a muscular-dystro-phy patient to walk. "Everybody recognizes that gene therapy is a very good idea," says Crystal. "And eventually it's going to work. "

单选题Questions 5～7 are based on the following news item, listen and choose the best answer.

单选题"She was America's princess as much as she was Britain's princess, "wrote the foreign editor of the normally sharp Chicago Tribune a week after the death in Paris of Diana, Princess of Wales. He was not far off the mark. For Americans have indeed taken posthumous possession of Britain's "People's Princess". What was happening? How was it that a nation whose school children are taught in history class to look down on the "tyranny" of the English monarchy, suddenly appeared so supportive of a member of the British royal family? Why was it that numerous American commentators sought to expand into touch the rumour that Diana had planned to move to the United States to live? Part of the answer lies in America's status as the celebrity culture par excellence. It is from their celebrities that many Americans derive their sense of nationhood. Their presidents must be celebrities in order to be elected. Writer and commentator Norman Mailer made the point after the last presidential election that Bill Clinton won because he projected the image of a Hollywood star, while Bob Dole lost because he came across as a supporting actor. What seems to have happened is that the inhabitants of the nation that produced Marilyn Monroe and Elvis Presley have found it almost impossible to accept that Princess Diana, the world's biggest, classiest contemporary celebrity by far, should have come from another country. Even that, many seemed to say to themselves, was merely an accident of birth; because in many ways she was so American. Her New Age preferences--the astrologers, the psychics, the aromatherapy--were closer to the style of former US First Lady Nancy Reagan than the House of Windsor. Her dieting and her visits to the gym were lifestyle options that were typically American. Her famous TV confession of adultery and her (purportedly unauthorized) tell-all biography were also hallmarks of the American celebrity approach. Like another former First Lady, Jackie Kennedy, she auctioned her dress-not in London or Pads, but New York. She visited America frequently and felt right at home there, reveling in the generous attentions of the rich and famous and delighting in the unreserved responsiveness of the public to her charms. For she seemed to have adapted brilliantly to another American invention: image manipulation, which all aspirants to political office in the US struggle to learn but which she appeared to have absorbed and refined naturally. She was, in short, a thoroughly modern woman and, like it or not, most of what is modern originates in the united States. But many Americans felt she also had more enduring qualities. Many viewed her as the incarnation of their country's dominant myth. As an editorial in the Miami Herald put it.. "She was an American dream, a superstar Cinderella with the polish of a natural-born socialite .... In a way she fulfilled the American dream~ to emerge from insignificance and overcome hardship and make something of herself. "Elaine Showalter, a student of American popular culture who teaches English at Princeton University, noted the difference between the dullness of Prince Charles and Diana's "very American sensibility". "We have a sense here in America that anything is possible, that you are not a predetermined person; that if you are a woman from whom nothing is expected but you want to make your life count, you can do it. She shared that spirit and that's why she appealed so much to Americans./

单选题{{B}}Text 2{{/B}} At dawn one morning in early May, Sean Cosgrove is stashing piles of maps, notes and photocopied documents in his gym bag before heading for West Milford High, a rural school in northernmost New Jersey. On his 30-minute commute, the young former investment banker tries to dream up new ways of lifting the monumentally forgettable Mexican War off the textbook page and into his students' imaginations. Can he invoke the storied memories of Robert E. Lee, who cut his first military exploits on the plains of Veracuz— or will he be met with thundering responses of "Who's Lee"? Should he raise James K. Polk out of the mystic chords of memory, and hope, for a nanosecond, that the kids will care about the first U. S president who stepped aside because he'd accomplished everything he wanted? Let's think some more. Well, there's always the Alamo. And hey, isn't that the teachers' parking lot up ahead? It's never an easy task. These big kids in big jeans and ball caps, come to his history classes believing that history is about as useful as Latin. Most are either unaware or unimpressed that the area's iron forges once produced artillery cannon for George Washington's army. Their sense of history orbits more narrowly around last month's adventures on "ShopRite Strip", the students' nickname for downtown West Milford, once a factory town, now a Magnet for middle-class vacationers. Cosgrove looks uncommonly glum as the thumbs through a stack of exams in the teachers' lounge. "I can't believe anyone in my class could think John Brown was the governor of Massachusetts," moans Cosgrove, 28, pointing to one student's test paper. He had to be sleeping for days on end. "The same morning, students in his college bound class could name only one U. S. Supreme Court justice—Clarence Thomas. All his wit, energy and beyond-the-textbook research can't completely reverse the students' poor preparation in history, their lack of general knowledge, their numbness to the outside world. It's the bane of history teachers at every level. When University of Vermont professor James Loewen asked his senior social-science majors who fought in the Vietnam War, 22 percent answered North and South Korea. Don't these kids even go to the movies?

单选题Belief We all believe in something or someone. We must believe,just as we must eat, sleep, and reproduce. Mankind has an insatiable need for and an irresistible attraction to a vast array of beliefs about gods and demons, magic and miracles, truth and falsehood, love and hate, similarity and difference. Implausible, even irrational ideas, have been cherished for centuries. Saints and other martyrs suffered indescribable pain and agony, even death, for their beliefs. Scientists have been put to death for their belief that the earth is round, or that there is an invisible force called gravity, or that the earth is not the center of the universe with the sun revolving around it, or that the blood circulates throughout the body, or that Man evolving around it, or that the blood circulates throughout the body, or that Man evolved from lower forms of life. Religious leaders have attracted millions of people with their version of how life began and how we must behave. If people do not believe in medicine and science, religion, education, government, and the social contract, chaos results and no society can tolerate that, which is why all societies impose order on their members. We must believe or face unbearable ambiguity and anxiety. Belief is faith and faith is trust and trust is security, predictability. Fear and hope are the twins that shape belief. We fear death, our enemies, illness, the known, the unknown, and punishment. Hope tells us that things will improve. We will not be defeated. We will succeed. It promises us a good life here and after death. Fear persuades us to believe that we can be protected, safe, if we join a group whose god is capable of holding evil at bay, then I cling to that group. We dare not, not believe. Furthermore, belief confers upon believers a special status: those who know the truth. Many people believe that their faith will help them to overcome sickness, fear, sorrow, joy, grief ect. , each trigger specific endocrinal secretions--hormones and neurotransmitters (adrenalin, serotonin or dopamine) that modify behavior. In order to control this torrent of endocrinal activity, many people turn to their faith because it convinces them that things will improve and that positive attitude cures the body to fight the invading bacteria or virus. Mind and body are totally integrated, supporting the notion that belief (faith) is a very powerful emotional force affecting physical behavior. Is the most effective belief system one that is composed of absolutes--unyielding, unvarying and eternal? The answer is yes, because when we eliminate doubt from a situation we feel secure, restored to balance, but if the belief system is science and is based on objective information without absolutes and requires a questioning attitude, not an accepting one as in most belief systems it unnerves people. They cannot handle the uncertainty, the lack of a God or some omnipotent overseer who eliminates doubt and reassures us that all is well and under control. Any system that offers definitive answers to complex human questions and problems: this is right, this is wrong, this is true, this is false--one question, one answer only, is very appealing. All beliefs require confirmation from an authoritative source whether that be a priest, a rabbi, a shaman, a family member, a special friend, an expert--one who commands obedience and respect an authenticator. Perhaps all belief is composed of the same elements in approximately the same proportions for even science requires a suspension of some disbelief, some uncertainty, however miniscule. Black Holes and the Big Bang are metaphoric truths derived from the physics we know now. But you have to believe, to have faith in the methods of science to gather information, to analyse and interpret it objectively in order to accept its conclusions. No one witnessed the Big Bang, or a Black Hole. These were inferred from careful study and analysis by many researchers. Can we devise an alternative to belief? Probably not. Belief pits one group against another. Muslims against Christians, Arabs against Jews, Catholics against Protestants, Serbs against Albanians, because each group insists that all must conform to their beliefs. Belief in an exclusive God divides men and has been a major cause of innumerable bloody wars. Not only religion divides people, but politics divides, socio - economic status divides, color divides and education divides us. In all cases, one group claims possession of the truth and the most sincere faith. All men consider themselves chosen, chosen by their God as the one and only, the best, the most cherished. We need our enemies. The only hope that I can imagine, and it is certainly a very fragile one, is that we all agree to believe whatever we wish and to worship as we choose, but we will accept every human as human as we are worthy of the same respect and care. Do unto others as you would have other do unto you. Simple, universal. Mankind is of a piece biologically, physiologically, and psychologically in that we all need love, peace, security ,food, clothing and shelter; we must all sleep, reproduce the species and we do it the same way with the same result. In the mirror you could see me and I could see you, but our cultures have taught us to notice differences in color, speech, clothing, food, marriage, belief in their own distinctively inflected way and that sets us apart. No one will take this suggestion very seriously. They never have, though most institutions have called for the same thing. This is true : your beliefs will separate you from me, may lead you to see me the enemy, a beliefs and my beliefs deny or denigrate the validity of your beliefs,but I will not be your enemy, your scapegoat, your excuse for venting suppressed anger and resentment you learned at home,in school, in your church or temple, in your neighborhood. I gain no wealth, no power, no wisdom at your expense, nor do I gain life in your death; we are bound together for our ambiguous stay on this whirling pellet in space. Belief is universal : soothing, comforting and uplifting, but it is the great divider. Perhaps we should take the witty and humorous advice of the American poet e. e. cummings:" Listen, there's a hell of a good universe next door; let's go "from his poem" pity this busy monster, mankind. /

单选题Questions 11—14 are based on the following talk.

单选题Managers spend a great deal of their time in meetings. According to Henry Mintzberg, in his book, The Nature of Managerial Work, managers in large organizations spend only 22 per cent of their time on meetings. So what are the managers doing in those meetings? There have conventionally been two answers. The first is the academic version: Managers are coordinating and controlling, making decisions, solving problems and planning. This interpretation has been largely discredited because it ignores the social and political forces at work in meetings. The second version claims that meetings provide little more than strategic sites for corporate gladiators to perform before the organizational emperors. This perspective is far more attractive, and has given rise to a large, add often humorous, body of literature on gamesmanship and posturing in meetings. It is, of course, true that meeting rooms serve as shop windows for managerial talent, but this is far from the truth as a whole. The suggestion that meetings are actually battle grounds is misleading since the feelings of meetings has far more to do with comfort than conflict. Meetings are actually vital props, both for the participants and the organization as a whole. For the organization, meetings represent recording devices. The minutes of meetings catalogue the change of the organization, at all levels, in a more systematic way than do the assorted memos and directives which are scattered about the company. They enshrine the minutes of corporate history, they itemize proposed actions and outcomes in a way which makes one look like the natural culmination of the other. The whole tenor of the minutes is one of total premeditation and implied continuity. They are a sanitized version of reality which suggests a reassuring level of control over events. What is more, the minutes record the debating of certain issues in an official and democratic forum, so that those not involved in the process can be assured that the decision was not taken lightly. As Dong Bennett, an administrative and financial manager with Allied Breweries, explains: "Time and effort are seen to have been invested in scrutinizing a certain course of action." Key individuals are also seen to have put their names behind that particular course of action. The decision can therefore proceed with the full weight of the organization behind it, even if it actually went through "on the nod". At the same time, the burden of responsibility is spread, so that no individual takes the blame. Thus, the public nature of formal meetings confers a degree of legitimacy on what happens in them. Having a view pass unchallenged at a meeting can be taken to indicate consensus. However, meetings also serve as an alibi for action, as demonstrated by one manager who explained to his subordinates, "I did what I could to prevent it — I had our objections minutes in two meetings. ' The proof of conspicuous effort was there in black and white. By merely attending meetings, managers buttress their status, while non-attendance can carry with it a certain stigma. Whether individual managers intend to make a contribution or not, it is satisfying to be considered one of those whose views matter. Ostracism, for senior managers, is not being invited to meetings. As one cynic observed, meetings are comfortingly tangible: "Who on the shop floor really believes that managers are working when they tour the works? But assemble them hehind closed doors and call it a meeting and everyone will take it for granted that they are hard at work." Managers are being seen to earn their corn. Meetings provide managers with another form of comfort too--that of formality. Meetings follow a fixed format: Exchanges are ritualized, the participants are probably known in advance, there is often a written agenda, arid there is a chance to prepare. Little wonder then, that they come as welcome relief from the upheaval and uncertainty of life outside the meeting room. Managers can draw further comfort from the realization that their peers are every bit as bemused and fallible as themselves. Meetings provide constant reminders that they share the same problems, preoccupations and anxieties, that they are all in the same boat. And for those who may be slightly adrift, meetings are ideal occasions for gently pulling them round. As Steve Styles, the process control manager(life services)at Legal＆General puts it: "The mere presence of others in meetings adds weight to teasing or censure and helps you to round up the strays'. ' Such gatherings therefore provide solace and direction for the management team a security blanket for managers. Meetings do serve a multitude of means as well as ends. They relieve managerial stress and facilitate consensus. For the organization, they have a safety--net--cum--robber-- stamping function without which decisions could not proceed, much less gather momentum. In short, meetings are fundamental to the well--being of managers and organizations alike.

单选题Questions 11 to 13 are based on the following introduction to Dr C. Henry Taylor. You now have 15 seconds to read Questions 11 to 13.

单选题{{B}}Text 2{{/B}} A rocket thruster based on an engine designed to power a lunar lander on an expedition to the Moon has been successfully tested by the Northrop Grumman aerospace company in the US. The thruster runs on a mix of liquid methane and liquid oxygen, which has the potential to be more efficient than other engines, but has never before been used to power or steer a spacecraft. Methane engines are a candidate for powering the liftoff vehicle NASA is developing to return astronauts from the lunar surface. Methane thrusters could be used for steering in space. Missions such as landing on and taking off from the Moon put stringent requirements on engines. Importantly, rockets must be liquid-fuelled so they can be shut down and restarted if needed. The Apollo lunar landers used exotic mixtures called "hypergolic" fuels, which ignite when they come into contact with a matched oxidizer. Because they are liquids at or near room temperature, hypergolic fuels don't require heavy cryogenics or pressurized tanks, and can be stored longer than liquid hydrogen and liquid oxygen (LOX) without boiling away. But the specific impulse—a measure of propulsion power—of hypergolic engines is only 260 to 310 seconds, compared to 425 to 455 seconds from liquid hydrogen and LOX. And hypergolic engines require the use of compounds such as nitrogen tetroxide and hydrazine, which are extremely toxic for astronauts and ground crews. Methane requires cooling to -161.6℃, close to the temperature of LOX, but well above the -252.9 degrees C needed for liquid hydrogen, reducing the mass of insulation and cooling equipment. Liquid methane is also denser than liquid hydrogen, so fuel tanks can be smaller than those for liquid hydrogen. And Northrop's test engine has already beaten the specific impulse of hypergolic fuels, although it can't match that of a liquid-hydrogen engine. The Northrop tests are a step toward answering NASA concerns about the ease of igniting methane, crucial for engine function, and have earned the company a 10-month contract for further engine development. "The engine far exceeded performance requirements," said Northrop programme manager Mark Trinidad. It was fired more than 50 times, a key capability for thrusters, which are used repeatedly. Meanwhile other teams are also working on more powerful methane/LOX engines suitable for lunar liftoff. Last year, NASA engineers fired a methane-LOX engine for 103 seconds and XCOR Aerospace test-fired a methane-LOX engine that generated 33,400 newtons (7,500 pounds) of thrust in shorter bursts lasting about one second. The XCOR engine is soon to be test-fired in a vacuum—a necessary test for space use. The company is developing another lower-powered methane/LOX engine for the MarsFlyer aircraft being developed by Aurora Flight Systems, which may one day take to the skies over the red planet.

单选题{{I}}Questions 11 - 13 are based on the following conversation. You now have 15 seconds to read Questions 11 - 13.{{/I}}