【单选题】

While the world's flu fighters have concentrated on countering the H1N1 swine flu, bird flu H5N1 has quietly continued to take its 【C1】______ on both poultry and humans. Last year, 17 countries, 【C2】______ from Germany to Japan, reported outbreaks of H5N1 in 【C3】______ poultry and wild birds; and the World Health Organization, which still says H5N1 causes a worldwide threat, recoded 72 human 【C4】______ , 32 of them fatal.

The major outbreak, entering its 【C5】______ year, is still in the developing countries of Asia. Indonesia 【C6】______ accounted for 19 of the 32 H5N1 deaths; Vietnam, 【C7】______ 5. But there are signs of 【C8】______ .
The number of human deaths has been 【C9】______ since peaking at 79 in 2006. And fewer countries reported outbreaks in 2009 than in 2008.
Partnership researchers compared notes on the effectiveness of control measures. Scientists reported that carefully 【C10】______ killing can be just as effective as wide spread killing, and less 【C11】______ . Others reported that reducing risk among those 【C12】______ backyard poultry has to be a community-wide effort, since changing the practices of 【C13】______ farmers has proven difficult.
In particular, Science Insider reported that a 3- year-old regional investigation network is making 【C14】______ in sorting out the role of wild birds. Some water birds 【C15】______ thought to be spreading the virus, such as the Asian open bill stork, are now known to quickly die of H5N1 infection, Wiriyarat says. But pas serine species , or perching birds, are apparently 【C16】______ the virus without ill effects, says an Asian zoologist. He also adds that there is a high 【C17】______ of outbreaks in poultry and passerine movements.
Wiriyarat says it is still 【C18】______ what is causing the outbreak, whether there is a natural storage for H5N1, and how the virus is 【C19】______ between domestic and wild birds. But while that research continues, the most effective way to reduce the amount of virus in 【C20】______ is to control outbreaks in poultry, he says.
【C1】
A．toll
B．money
C．fee
D．tuition