gwd 16-38求教nn

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.

E followed by an outbreak. the condition happens before outbreak

so E.

Farmer can not routinely use vaccine because outbreak is unpredictable. E) outbreak can be predictable. Thus E is correct