求教高手

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.

请问高手为何这个题不选A而选C呢？