请教一个阅读的问题。。。

niclively

刚开始复习GMAT.... 对阅读的理解有限.. 求大家帮忙解答一下这个问题.. 我怎么都推不出来啊 感觉这是一篇非常简单的阅读题目....

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 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.
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?
(A) The deer population was smaller in the late nineteenth century than in the mid-twentieth century.
(B) Interest in outdoor recreation began to grow in the late nineteenth century.
(C) In recent years the suburbs have stopped growing.
(D) Outdoor recreation enthusiasts routinely take measures to protect themselves against Lyme disease.
(E) Scientists have not yet developed a vaccine that can prevent Lyme disease.

这题感觉跟逻辑很像.. 答案选A 可是如果A成立为什么B不成立呢？我都没有看出时间点是怎么推出来的.....
谁教我一下啊。。谢谢~~

cristophor

我也是新人,我的理解是

十九世纪末零星的发生了lyme desease,而最近（二十世纪中期）在美国的一些地方lyme disease开始爆发了。很大一部分原因是因为鹿数量增长以及人们在鹿栖息地的户外活动增加所致。

所以B项说十九世纪末 人们的户外活动增加就错，因为那样 desease 应该在十九世纪末就有增长的趋势，而不是等到最近才重新突然爆发。