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1. According to the author, what may be the possible carriers of bird flu?
2. The main sources of influenza viruses in lake water are__________, which may stay infectious for up to 30 days.
3. By saying "bird flu viruses appear to exist in ducks in a low-pathogenic form" (Para. 6 ), the author suggests that infection
4. On what condition can the birds spread the influenza through migration?
5. According to the study team, __________is a practice that can encourage transmission of the bird flu.
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