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Outbreaks of Rift Valley fever occur irregularly in East Africa, several years apart. When outbreaks do occur, they kill thousands of cattle. A livestock vaccine against the disease exists but is rarely used. It is too expensive for farmers to use routinely, and since it is not effective until a month after vaccination, administering it after an outbreak begins helps very little. Nevertheless, experts predict that use of the vaccine will increase significantly within the next few years.

Which of the following, if true, provides the strongest justification for the experts' prediction?

正确答案: E

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楼主
发表于 2005-7-25 09:23:00 | 显示全部楼层
以下是引用kingsoft在2004-6-13 14:03:00的发言:

   选E


   原文推论:1)疫苗昂贵,2)疫苗使用一个月以后才生效(发病后使用效用不大)——》疫苗不常用


                     专家却说:以后这个疫苗会广泛应用,问支持专家


   E说那种病之前的2-5个月的天气条件几乎不变,就是说在这种病来之前的2-5月就可知道这种病即将爆发,然后就能用疫苗


    其他选项无关


要support专家的观点,有两种途径:一是对条件1的否定,即价格不贵,二是对条件2的否定,即一个月前就可以避免其作用要在一个月后才能发挥的缺点,本题E答案是对2的取非加强。

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