2. 外语
  3. For several years,scientists have been testing a substance called interferon(干扰素),a potential wonder drug that is proving to be

For several years,scientists have been testing a substance called interferon(干扰素),a potential wonder drug that is proving to be

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问题     For several years,scientists have been testing a substance called interferon(干扰素),a potential wonder drug that is proving to be effective in treating a variety of ailments,including virus infections,bacteria infections,and tumors. To date,the new drug has provoked no negative reaction of sufficient significance to discourage its use. But in spite of its success,last year only one gram Was produced in the entire world.
    The reason for the scarcity lies in the structure of interferon. A species of specific protein,the interferon produced from one animal species cannot be used in treating another animal species. In other words, to treat human beings,only interferon produced by human beings may be used. The drug is produced by infecting white blood cells with a virus. Fortunately.it is so powerful that the amount given each patient per injection is very small.
    Unlike antibiotics, interferon does not attack germs directly. Instead.it makes unaffected cells resistant to infection,and prevents the multiplication of viruses within cells.
    As you might conclude,one of the most dramatic uses of interferon has been in the treatment of cancer. Dr. Hans Strander,research physician at Sweden’s famous Karolinska Institute,has treated more than one hundred cancer patients with the new drug. Among a group of selected patients who has undergone surgical procedures for advanced cancer, half were given interferon. The survival rate over a three-year period was 70 percent among those who were treated with interferon as compared with only 10 to 30 percent among those who have received the conventional treatments.
    In the United States,a large-scale project supported by the American Cancer Society is now underway. If the experiment is successful,interferon could become one of the greatest medical discoveries of our time.
Interferon has not been widely used because it is_____.
选项 A、still very dangerous
B、not yet available in the United States
C、difficult to produce in large quantities
D、not effective for human beings
答案B
解析 推理题。解题点在最后一段。文章最后提到“a large-scale project supported by the AmericanCancer Society is now underway．If the experiment is successful…．”。据此可知，该药在美国尚在试验当中。既然是试验，自然就不可能大范围内使用了。所以正确答案是B选项。其它选项均可以在原文中找到相应的信息点，如A选项，文中未提到该药是危险的；C选项，文中没有说干扰素难以大量生产；D选项，瑞典的试验表明，与常规治疗方法相比，干扰素的治疗效果是明显的，故D项不对。
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