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  3. Although we already know a great deal about influenza, it is difficult for epidemiologists(流行病学家), who study infectious disease,

Although we already know a great deal about influenza, it is difficult for epidemiologists(流行病学家), who study infectious disease,

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问题     Although we already know a great deal about influenza, it is difficult for epidemiologists(流行病学家), who study infectious disease, to【C1】______when and where the next flu epidemic will occur, and how【C2】______it will be. There are three kinds of influenza virus, known as A, B and C. Influenza C virus is relatively stable and causes mild【C3】______that do not spread far through the population. The A and B types are【C4】______, and are responsible for the epidemics that cause frequent concern. Following any virus attack, the human body builds up antibodies which confer(给予)immunity to that strain of virus, but a virus with the capacity to change its character is able to bypass this【C5】______. Variability is less developed in the influenza B virus, which affects only human beings. An influenza B virus may cause a widespread epidemic but will have little effect if【C6】______into the same community soon afterwards, since nearly everyone will have built up antibodies and will be immune. The influenza A virus, which【C7】______affects animals, is extremely unstable and is responsible for some of the worst outbreaks of the disease, such as the unparalleled pandemic, or world epidemic. Accurate prediction is difficult because of the complication of the【C8】______. A particular virus may be related to one to which some of the population have【C9】______involved immunity. The extent to which it will spread will depend on factors such as its own strength, or virulence, the ease with which it can be【C10】______and the strength of the opposition it encounters. Scientists, however, have a reliable general picture of the world situation, according to which we may take some precautions.
A)partially I)epidemics
B)guess J)also
C)factors K)attacks
D)equally L)introduced
E)generally M)unstable
F)protection N)infections
G)transmitted 0)predict
H)severe
【C5】
选项
答案F
解析 此处应填名词。由this和句中的转折关系可知，所填词指的是抗体对病毒的免疫作用，因此选F)protec—tion“保护”。就选项K)attacks而言，人体对病毒免疫功能的实现包含对病毒的攻击，但是根据this可知K)at—tacks的复数形式在这里不合适，故排除。
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