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  3. Although genetic mutations in bacteria and viruses can lead to epidemics, some epidemics are caused by bacteria and viruses that

Although genetic mutations in bacteria and viruses can lead to epidemics, some epidemics are caused by bacteria and viruses that

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问题     Although genetic mutations in bacteria and viruses can lead to epidemics, some epidemics are caused by bacteria and viruses that have undergone no significant genetic change. In analyzing the latter, scientists have discovered the importance of social and ecological factors to epidemics. Poliomyelitis, for example, emerged as an epidemic in the United States in the twentieth century, by then, modern sanitation was able to delay exposure to polio until adolescence or adulthood, at which time polio infection produced paralysis. Previously, infection had occurred during infancy, when it typically provided lifelong immunity without paralysis. Thus, the hygiene that helped prevent typhoid epidemics indirectly fostered a paralytic polio epidemic. Another example is Lyme disease, which is caused by bacteria that are transmitted by deer ticks. It occurred only sporadically during the late nineteenth century, but has recently become prevalent in parts of the United States, largely due to an increase in the deer population that occurred simultaneously with the growth of the suburbs and increased outdoor recreational activities in the deer’s habitat. Similarly, an outbreak of dengue hemorrhagic fever became an epidemic in Asia in the 1950s because of ecological changes that caused Aedesaegypti, the mosquito that transmits the dengue virus, to proliferate. The stage is now set in the United States for a dengue epidemic because of the inadvertent introduction and wide dissemination of another mosquito, Aedesalbopictus.
Which of the following, if true, would most strengthen the author’ s assertion about the cause of the Lyme disease outbreak in the United States?
选项 A、The deer population was smaller in the late 19th century than in the mid-20th century.
B、Interest in outdoor recreation began to grow in the late 19th century.
C、In recent years the suburbs have stopped growing.
D、Scientists have not yet developed a vaccine that can prevent Lyme disease.
答案A
解析 细节题。题目问的是如果是真的话，下面哪一项能够加强作者关于发生于美国的莱姆病病因的论述?短文最后说到，莱姆病间歇发生于19世纪晚期的美国，最近在美国部分地区又开始传播，其起因是由于鹿蜱的增加以及人们接触鹿蜱的机会更多。可知，19世纪鹿的总数比20世纪的少，而鹿蜱更多意味着莱姆病发病的概率更高，故选A。
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