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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?

1. Rift Valley fever is spread by mosquitoes, but each outbreak is so widespread that it is impractical to control it by using insecticides.
2. When an outbreak of Rift Valley fever occurs, unaffected countries often refuse to import livestock from the countries affected by the outbreak.
3. 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.
4. 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.
5. 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.

怎么会选E？

不明白！

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