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题库 / Prep2008E2-CR-114
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?
Rift Valley fever is spread by mosquitoes, but each outbreak is so widespread that it is impractical to control it by using insecticides.
When an outbreak of Rift Valley fever occurs, unaffected countries often refuse to import livestock from the countries affected by the outbreak.
It would take less than a month for producers of the vaccine to adjust their production operations to cope with a large increase in demand.
Many cattle farmers in East Africa are nomadic or live in remote villages, and such farmers, who have little access to modern veterinary medicine, are particularly hard hit by outbreaks of Rift Valley fever.
Recently published research has shown that certain identifiable climatic conditions are almost invariably followed, within two to five months, by an outbreak of Rift Valley fever.
情景：裂谷热经常在东非发生，每次发生都会令数千头小牛受灾。有一种防治裂谷热的疫苗，价格比较贵，并且在注射一个月后才能起效，所以这种疫苗也不能让情况变好。但专家预测，接下来疫苗会被明显使用。
答案预估：
直接解释为什么接下来疫苗的使用会明显增加。
选项分析：
A选项：裂谷热是由蚊虫传播的，但是每一次爆发都太广泛了以至于不可能用杀虫剂来控制。无论怎么控制Rift Valley fever这种病的传染源，都不能解释为什么疫苗会被使用。
B选项：当裂谷热爆发时，没有被感染的国家会拒绝进口被感染国家的家禽。本选项描述的是爆发后给被感染的国家带来的坏处，并不能解释为什么疫苗会被使用。
C选项：做疫苗的人用不到一个月的时间就可以通过调整生产操作流程来满足上涨的需求。推理文段的结论是疫苗的需求不会上涨，这个选项已经说到了上涨后的情况了。
D选项：在东非很多养牛的人是流浪的或者住在总是迁徙的村子里，这些农民会受到非常严重的由裂谷热带来的打击。本选项描述的是谁更容易受到伤害的问题，而不是会不会用疫苗的问题。
E选项：Correct. 最近出版的研究显示某些特定的可识别的气候条件出现后，在2~5个月内，一定会出现裂谷热的爆发。如果本选项成立，则农民可以至少提前两个月预测到裂谷热的爆发，这样就可以在特定的可识别的气候条件出现时，先给牛注射该疫苗，使牛免疫于裂谷热，所以农民们可能会选择给牛接种该疫苗，可以成为答案。
错选成B，B没有解决本质问题，即便为了输出要给畜牲打疫苗，但是疫苗生效时间还是一个月，所以还是来不及。所以B并没有什么用。还是E最优秀，如果一个月的时间问题得以解决，那么疫苗就会解决病毒爆发这个问题了。
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