单选题{{I}} You will hear 10 short dialogues. For each dialogue, there is one question and four possible answers. Choose the correct answer--A, B, C or D, and mark it in your test booklet. You will have 15 seconds to answer the question and you will hear each dialogue ONLY ONCE.Now look at Question 1.{{/I}}

单选题 In the 18th century, New York was smaller than Philadelphia and Boston. Today it is the largest city in America. How to explain the change in its size and importance? To answer this question we must consider certain facts about geography, history and economics. Together these three will explain the huge growth of America's most famous cities. The map of the Northeast shows that four of the most heavily-populated areas in this region are around seaports. At these points materials from across tile sea enter America, and the products of the land are sent there for export across the sea. Economists know that places where transportation lines meet are good places for making raw materials into completed goods, That is why seaports often have cities nearby. But cities like New York needed more than their geographical location in order to become great industrial centers. Their development did not happen simply by chance. About 1815, when many Americans from the east coast had already moved to the west. trade routes from the ports to the central regions of the country began to be a serious problem, The slow wagons of that time. drawn by horses or oxen, were too expensive for moving heavy freight very far. Americans had long admired Europe's canals. In New York State a canal seemed the best solution to the transportation problem From the eastern end of Lake Erie all the way across the state to the Hudson River there is a long trip of low land Here the Erie Canal was constructed. After working for several years it was completed in 1825. The canal produced an immediate effect. Freight costs were cut to about one-tenth of what they had been. New York City, which had been smaller than Philadelphia and Boston, quickly became the leading city of the coast. In later years, transportation routes on the Great Lakes were joined to routes on the Mississippi River. Then New York City became the end point of a great inland shipping system that emended from the Atlantic Ocean far up to the western branches of the Mississippi. The new railroads made canal shipping not as important as before, but it tied New York even more closely to the central regions of the country. It was easier for people in the central states to ship their goods to New York for export overseas. Exports from New York were greater than imports. Consequently, shipping companies were eager to fill their ships with passengers on the return trip from Europe. Passengers could come from Europe very cheaply as a result. Thus New York became the greatest port for receiving people from European countries. Many of them remained in the city. Others stayed in New York for a few weeks, months or years, and then moved to other parts of the United States. For these great numbers of new Americans. New York had to provide homes, goods and services. Their labor helped the city become great

单选题It can be concluded from the author's remarks that

单选题Which is tree according to the passage?

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单选题A newly published AIDS study could open another front in the battle against HIV infection by showing that gene therapy can be used to stop infected cells from spreading the deadly virus, researchers said. In a test-tube experiment believed to be the first of its kind, researchers based at Children's Hospital of Philadelphia were able to block the operation of the "tat" gene that allows HIV to spread throughout the body from infected cells. Up to now, genetic AIDS research has concentrated on finding ways to help healthy cells withstand the ravages of the HIV virus that infects an estimated 16,000 new victims a day, mainly in the developing world. But by working with human cells already infected with HIV, the team was able to reduce the tat gene's virus-replicating functions by 80 percent to 90 percent, according to findings published in the journal Gene Therapy. That, researchers said, raises the possibility of a new gene therapy approach capable of supplementing the current drug-based treatment known as highly active antiretroviral therapy, or HAART, which is used to stop HIV infection from becoming full-blown AIDS. In recent studies, HAART has proved to be a costly drug regimen that poses serious side effects for HIV patients while delivering questionable results. "This is proof of the concept that HIV replication could be inhibited by a genetic approach, though we're not at 100 percent yet," said Dr. Stuart Starr, a study coauthor and chief of immunologic infectious diseases at Children's Hospital. "Everyone thinks of an antiviral approach, or an immunologic approach (to HIV). This adds another option into the equation that could become more important as other options prove not to be totally successful." Key to the study was an artificially produced "antitat" gene provided by the Washingtonbased Research Institute for Genetic and Human Therapy. Children's Hospital researchers used a mouse retrovirus to deliver the antitat gene into HIV-infected U-1 and ACH-2 cells, which were developed in the lab from the tissues of living HIV patients. They found that when the antitat protein combined with the tat gene, it successfully inhibited the gene's operation without disturbing healthy cells or causing toxic side-effects. The study, funded by a private foundation, also found that the introduction of the antitat gene prolonged the survival of immune-system cells called CD4+T lymphocytes. Starr said researchers have entered preliminary discussions with a New England-based primate center, where animal experiments could be carried out on infected macaque monkeys. If animal experiments proved successful, the Children's Hospital team would hope to have a gene therapy treatment ready for human clinical trials in three to four years.

单选题New research from Australia supports the belief that many pet owners have—it shows that pets are good for your health. The findings of this new study suggest that people who have pets are at less risk from heart disease than those who do not. Ironically, this latest study on pets was intended to explode the myth that pets are good for your health. Earlier research on the benefits of owning pets received a lot of publicity, but the results were not good enough to convince the more skeptical doctors. The new research was carried out over three years and examined 6000 people, the largest group yet involved in such a study. They took tests that measured a variety of different factors known to be involved in heart disease—blood pressure, and blood levels of cholesterol (胆固醇) and triglyceride (甘油三酯). Also, people were asked about their lifestyles. The 800 people who owned pets had lower levels on each of the factors measured than those who did not own pets. The differences were even greater than those found in similar studies on people who switched to vegetarian diets or took up exercise. The study also showed that it did not matter what kind of pet was owned—a cat was as good as a dog—so the benefits could not be attributed to the exercise involved in walking a dog. The question is, just how do pets manage to make their owners more healthy? The obvious answer is that they make their owners feel more relaxed and happy. After all, what better way of getting rid of all that tension than by walking the dog or stroking the cat? However, it is not that simple. While there is some evidence that an unhappy event, such as the death of a partner, can be bad for a person's health, at the moment there is little evidence that having good relationships has a positive effect on health. As long as the exact way that pets make their owners healthier is unknown, many doctors will be reluctant to prescribe a pet instead of a pill for their patients. Nevertheless, the Australian scientist who organized this study commented that if a new drug was available that was as effective as simply having a pet, then this drug would undoubtedly be considered a breakthrough in the control of heart disease.

单选题______ percent of all cancers could be averted if people ate more fruits, vegetables, and plant-based foods and minimized high-fat, high-calorie edibles.

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单选题There is ______ "h" in the word" hair." [A] a [B] an [C] the

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单选题Questions 14～16 are based on the following talk about a wife's complaint. You now have 15 seconds to read Questions 14～16.

单选题 {{I}} Questions 14—16 are based on the following dialogue about a phone call. You now have 15 seconds to read Questions 14—16.{{/I}}

单选题What happened in 1920?