阅读理解

　　On June 5,1981 the Centers for Disease Control in Atlanta, U．S．announced the presence of a rare, infectious disease in five American homosexuals(同性恋)．Soon doctors were finding similar cases all over the country and the world．The AIDS epidemic(流行病)had officially begun．By 1983 it was clear that AIDS had spread around the world．More than twenty years later, AIDS has left twenty-six million dead and another forty million infected．AIDS has become the worst medical disaster ever experienced by mankind．

　　Hundreds of young people between the ages of 20 and 45 died each week during the early years of the U．S．AIDS．More than 600 000 cases of AIDS have been reported since 1981 in the United States, and it is estimated that there may be as many as 900 000 Americans infected with HIV．

　　Though the rate of HIV infections continues to increase in the United States, the number of AIDS cases has fallen sharply since 1996, when antiretroviral drugs came into the market．Unfortunately, the AIDS epidemic continues today in Africa and much of Asia, where antiretroviral treatment is not available and health care is far from enough．AIDS is the fourth leading cause of death worldwide, and the No．1 cause of death due to infectious disease．

　　HIV, the virus that causes AIDS, was first separated in 1983 by a team at the Pasteur Institute in Paris．That discovery made it possible to develop a test for AIDS and trace back to victims who may have died before doctors were aware of the disease．

　　However, scientists still don’t know exactly how and where AIDS started．Finding the source of AIDS could be important in developing a vaccine(疫苗)and be important in mapping the future course of the epidemic．

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　　On June 5, 1981 the Centers for Disease Control in Atlanta, U．S．announced the presence of a rare, infectious disease in five American homosexuals(同性恋)．Soon doctors were finding similar cases all over the country and the world．The AIDS epidemic(流行病)had officially begun．By 1983 it was clear that AIDS had spread around the world．More than twenty years later, AIDS has left twenty-six million dead and another forty million infected． AIDS has become the worst medical disaster ever experienced by mankind．

　　Hundreds of young people between the ages of 20 and 45 died each week during the early years of the U．S．AIDS．More than 600,000 cases of AIDS have been reported since 1981 in the United States, and it is estimated that there may be as many as 900,000 Americans infected with HIV．

　　Though the rate of HIV infections continues to increase in the United States, the number of AIDS cases has fallen sharply since 1996, when antiretroviral drugs came onto the market．Unfortunately, the AIDS epidemic continues today in Africa and much of Asia, where antiretroviral treatment is not available and health care is far from enough．AIDS is the fourth leading cause of death worldwide, and the No．1 cause of death due to infectious disease．

　　HIV, the virus that causes AIDS, was first separated in 1983 by a team at the Pasteur Institute in Paris．That discovery made it possible to develop a test for AIDS and trace back to victims who may have died before doctors were aware of the disease．

　　However, scientists still don't know exactly how and where AIDS started．Finding the source of AIDS could be important in developing a vaccine(疫苗)and be important in mapping the future course of the epidemic．

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阅读理解

　　Terraforming(Earth-forming)other planets, also known as planetary engineering(行星工程), seems like a task still centuries away for mankind to accomplish．However, it is a vigorous topic that attracts both popular and scientific interest．Why should the possibility of terraforming other planets be studied when it may be centuries before we know enough to even decide if it’s a good idea?

　　Mankind is getting more and more hard facts about other planets．The atmosphere of Venus has been explored; robots have surveyed the surface of Mars; Mercury, Jupiter and Saturn have been studied by spacecraft．Speculations have been answered; new questions have been raised, and enough hard data is right now becoming available to allow us to make the first attempt of planetary engineering．

　　In the past, people with excellent ideas about terraforming have kept them to themselves, or buried them in a desk drawer because they did not realize that anyone else was interested．But now, a wide circle of people has begun to do this kind of work．For instance, NASA funded a project on transforming Mars．

　　There are several strong reasons which demand that the possibilities of terraforming be studied carefully．First, it’s an exciting idea of a possible future for human beings．Such thinking has a valuable role in providing options for our future directions．Secondly, the techniques of terraforming will also help contemporary technologies in weather and climate control．Thirdly, such study may assist us in detecting any possible existence of extraterrestrial intelligence(SETI, The Search for Extraterrestrial Intelligence, 地外文明搜索)and alien(异己的)civilizations on other planets．

　　Though the mission is far beyond our reach at the moment, we should at least keep our options open．Through debate and study on this subject, the possibility of rebuilding other planets to make them suitable homes for people may come true some day in the future．

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