[求助]og紫色阅读第6题

librahjx

Although genetic mutations in bacteria and viruses ca n 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 9rovided 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 1950's because of ecological changes that caused Aedes aegypti，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，Aedes albopictus．

 

Questions6-11 refer to the passage above.

6. The passage suggests that a lack of modern sanitation would make which of the following most likely to occur?

(A)  An outbreak of Lyme disease

(B)  An outbreak of dengue hemorrhagic fever

(C)  An epidemic of typhoid

(D)  An epidemic of paralytic polio among infants

(E)  An epidemic of paralytic polio among adolescents and adults

我始终不太明白为什么不是Ｃ而是D

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 9rovided lifelong immunity without paralysis．

加粗那里不是说没有modern sanitation ,  infection就会发生在infancy么？

steviori

正确答案是C

D错，infants did not typically suffer paralysis with polio

lalaxiaowu

the hygiene that helped prevent typhoid epidemics indirectly fostered a paralytic polio epidemic. 答案在这句里面