Lofgren’s disease has been observed frequently in commercially raised cattle but very rarely in chickens. Both cattle and chickens raised for meat are often fed the type of feed that transmits the virus that causes the disease. Animals infected with the virus take more than a year to develop symptoms of Lofgren’s disease, however, and chickens commercially raised for meat, unlike cattle, are generally brought to market during their first year of life.
Which of the following is most strongly supported by the information provided?
A. The virus that causes Lofgren’s disease cannot be transmitted to human beings by chickens.
B. There is no way to determine whether a chicken is infected with the Lofgren’s disease virus before the chicken shows symptoms of the disease.
C. A failure to observe Lofgren’s disease in commercial chicken populations is not good evidence that chickens are immune to the virus that causes this disease.
D. An animal that has been infected with the virus that causes Lofgren’s disease but that has not developed symptoms cannot transmit the disease to an uninfected animal of the same species.
E. The feed that chickens and cattle are fed is probably not the only source of the virus that causes Lofgren’s disease.
1) Lofgren’s disease has been observed frequently in commercially raised cattle but very rarely in chickens. (提出现象，牛多、鸡少)
2) Both cattle and chickens raised for meat are often fed the type of feed that transmits the virus that causes the disease. (牛鸡同食)
Animals infected with the virus take more than a year to develop symptoms of Lofgren’s disease, however, and chickens commercially raised for meat, unlike cattle, are generally brought to market during their first year of life.（鸡先上市，按理说应该比牛感染多）
A failure to observe Lofgren’s disease in commercial chicken populations is not good evidence that chickens are immune to the virus that causes this disease.
我觉得C选项是对的。
但是，我觉得E选项也没有错啊：
E. The feed that chickens and cattle are fed is probably not the only source of the virus that causes Lofgren’s disease. 解释了牛多鸡少的其他可能原因
谁能帮忙解释E?作者: yoyo9012 时间: 2010-9-16 06:39
vote for c
ls 说的是削弱题设结论的可能性
但题目问的是support by 即结论题型
故不能出现与原文无关的答案
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