GWD-12-Q38:

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.

I have no idea why E is KEY. My answer is B . Please help.

 E说这个fever总是跟着某种特定的可以确定的天气变化的，一般总是在2-5个月以后爆发。

我想E要说的是这个fever就是可以预防的了，因为必须要打满一个月的疫苗才能有效，如果那个天气来了，那么农民只要马上开始打疫苗，打一个月，疫苗起效了但是fever最少还要一个月才能到。这样奶牛就死的少了。

但是E也不是一个很好的答案，个人以为，因为这必须一个前提，那就是这个certian identifiable 在next few years里面会出现（因为文章说这个fever爆发的irregularlly，所以我觉的我有理由怀疑这个certian identifiable 在next few years可能不会出现，这样的话，作者结论未必成立）

Anyway， E is the only option for us,just pick it up in the testime, but in the disscussing, I think it is an other story.

B中的unaffected countries是一个无关信息。

这是一道Resovle the paradox, 原文的paradox在于vaccine在接种一个月以后才有效，在疾病爆发以后接种没什么用处。然后专家预测在今后五年这种vaccine的使用会大规模增加。

看完题，有种感觉，应该在时间上面做文章。

E中说了，在今后两个月到五个月间，会有一次大规模的疾病爆发。 那么近期（疾病爆发一个月以前）给牲口接种这种疫苗就合理了。

Thanks, now I agree on E.

My reasoning for B was that

Since unaffected countries often refuse to import livestock from affected countries when the fever occurs, the farmers have to vaccine their cattle, otherwise they even cannot export the livestock other than cattle. In order for other livestock to be exported, the farmers will be doing what the experts predict to do.