2. 外语
  3. The H5N1 virus does not usually infect humans. In 1997, however, the first case of【S1】______ from a bird to a human was seen du

The H5N1 virus does not usually infect humans. In 1997, however, the first case of【S1】______ from a bird to a human was seen du

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问题     The H5N1 virus does not usually infect humans. In 1997, however, the first case of【S1】______  from a bird to a human was seen during an outbreak of bird flu in poultry in Hong Kong. The virus【S2】______  severe respiratory illness in 18 people, 6 of whom died. Since that time, there have been other cases of H5N1 infection among humans. Most recently, human cases of H5N1 infection have【S3】______  in Thailand, Vietnam and Cambodia during large H5N1 outbreaks in poultry. The death【S4】______  for these reported cases has been about 50 percent. Most of these cases occurred from【S5】______  with infected poultry or contaminated surfaces; however, it is thought that a few cases of human-to-human spread of H5N1 have occurred.
    So far, spread of H5N1 virus from person to person has been【S6】______  and spread has not continued【S7】______  one person. However, because all influenza viruses have the ability to change, scientists are【S8】______  that the H5N1 virus could one day be able to infect humans and spread easily from one person to another. Because these viruses do not commonly infect humans, there is【S9】______  or no immune protection against them in the human population. If the H5N1 virus were able to infect people and spread easily from person to person, an "influenza pandemic" (worldwide outbreak of disease) could begin. No one can predict when a pandemic might occur. However, experts from around the world are watching the H5NI situation in Asia very【S10】______  and are preparing for the possibility that the virus may begin to spread more easily and widely from person to person.

A) number         B) concerned         C) caused            D) over  
E) spread         F) contact           G) beyond            H) absent
I) forgotten      J) little            K) occurred          L) slightly
M) rare           N) closely           O) rate
【S3】
选项
答案K
解析 occur出现，发生。
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