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It could take 4-6 months before the first batch（批）of vaccines （疫苗）are available to fight A/H1N1 flu...
题目内容：
It could take 4-6 months before the first batch（批）of vaccines （疫苗）are available to fight A/H1N1 flu ________ as swine flu, WHO officials said.
A. known B. to know C. knowing D. having known
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