It has become a cliche among doctors who deal with AIDS that the only way to stop the epidemic is to develop a vaccine against HIV, the virus that causes it. Unfortunately, there is no sign of such a thing becoming available soon. The best hope was withdrawn from trials just over a year ago amid fears that it might actually be making things worse. As a result, vaccine researchers have mostly gone back to the drawing board of basic research. Meanwhile, the virus marches on. Last year, according to UNAIDS, the international body charged with combating it, 2.7 million people were infected, bringing the estimated total to 33 million. Reuben Granich and his colleagues at the World Health Organization (WHO), though, have been exploring an alternative approach. Instead of a vaccine, they wonder, as they write in The Lancet, whether the job might be done with drugs. In the spread of any contagious disease, each act of infection has two parties, one who already has the disease and one who does not. Vaccination works by treating the uninfected individual prophylactically (预防地). Since it is" impossible to say in advance who might be exposed, that means vaccinating everybody. The alternative, as Dr. Granich observes, is to treat the infected individual and thus stop him being infectious. For this to curb an epidemic would require an enormous public-health campaign of the sort used to promote vaccination. But that campaign would be of a different kind. It would have to identify all (or, at least, almost all) of those infected. It would then have to persuade them to undergo not a short, simple vaccination course, but rather a drug regime that would continue indefinitely. The first question to ask of such an approach is, could it work in principle It is this that Dr. Granich and his colleagues have tried to answer. Using data from several African countries, they have constructed a computer model to test the idea. In their ideal world, everyone over the age of 15 would volunteer for testing once a year. If found to be infected, they would be put immediately onto a course of what are known as first-line antiretroviral drugs (ARVs). These are reasonably cheap, often generic, pharmaceuticals (医药品) that, although they do not cure someone, do lower the level of the virus in his body to the extent that he suffers no symptoms. They also -- and this is the point of the study -- reduce the level enough to make him unlikely to pass the virus on. For the 3% or so of people per year for whom the first-line ARVs do not work, more expensive second-line treatments would be used. We can infer from the word "ideal" in the last paragraph that ______.

A. researchers’ design is too unrealistic
B. everyone dreams an ideal world they can test
C. people over 15 receiving tests once a year is just what researchers conceived
D. it is impossible for everyone over 15 to test once a year