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x 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 , 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. 文章精要 文章重点介绍了禽流感病毒的主要携带者以及其可能的传播途径、变异后果等，还指出迁徙的鸭子可能会将禽流感传染到尚未发现H5N1型禽流感案例的北美大陆。 1.Wild ducks and other migratory birds./Ducks，geese and wading birds. 文章开头指出，野鸭以及其他迁徙鸟类可能是致命性禽流感的重要携带者，由此可得答案;第二段又提到，鸭子可能在传染野鸟，而鹅和涉水鸟也可能是病毒的携带者，由此也可得答案。 2.bird feces 根据题干中的关键词lake water和30 days定位到第四段，可知研究表明，湖水中的流感病毒一般是通过鸟粪传播的，这些病毒的传染性可长达30天。 3.doesnt usually lead to severe illness and death | 
