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  3. For several years, scientists have been testing a substance called interferon, a potential wonder drug that is proving to be eff

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

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问题     For several years, scientists have been testing a substance called interferon, 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 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 potent 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 Karohnska Institute, has treated more than one hundred cancer patients with the new drug. Among a group of selected patients who had undergone surgical procedures for advanced cancer, half were given conventional treatments and the other 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 had 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C
解析 文中第二段前三句说：“这种供不应求的原因在于干扰素的构成结构上。作为一种特殊种类的蛋白质，从一种动物身上产生出来的干扰素不能用在另一种动物身上。换句话说，用于治疗人体疾病的干扰素只能从人体内产生并提取。”由此我们可以推断出，在人体内生产干扰素是有难度的，因而大批量生产是困难的。因此选项C正确。本题通过排除法也可以确定答案。选项A说使用干扰素仍然非常危险，这不符合文中第一段内容，可排除；选项D说干扰素对人体无效，同样也与文中第一段内容不符，亦可排除；选项B说在美国仍没有使用干扰素，我们在文中最后一段得知，美国正在进行一项大规模的工程来生产干扰素，根据常识推断，干扰素一定在美国试用过，否则不可能进行大规模生产。由此选项B可以排除。
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