Critical Reasoning

Outbreaks of rift valley occur irregularly in east africa, several years apart. When the outbreaks do occur, they kill thousands of cattle. A livestock vaccine against the disease exists but is rarely used. It is too expensive for farmer to use routinely, and since it is not effective untill a month after vaccination, administtering it after an outbreak begins helps very little. Nevertheless, experts predict that use of the vaccine will increase significantly withing the next few years.

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

Rift Valley fever is spread by mosquitos, 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 the 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.

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I came across the above question while giving the GMATPrep practise test 1. the answer to the above question is the last option. I need some help in understanding why it is so, and why the other options are not the right answer choices.

thanks in advance!