A recent study suggests that Alzheimer' s disease, which attacks the human brain, may be caused by a virus. In the study, blood from 11 volunteers, each of whom had the disease, was injected into rats. The rats eventually exhibited symptoms of another degenerative neurological disorder, Creutzfeldt-Jakob disease, which is caused by a virus. This led the scientist who conducted the study to conclude that Alzheimer' s disease might be caused by a virus. Which one of the following statements, if true, would most strengthen the scientist's hypothesis that Alzheimer's disease is caused by a virus? ["Creutzfeldt-Jakob disease affects only motor nerves in rats' limbs, not their brains.", 'The virus that causes Creutzfeldt-Jakob disease in rats has no effect on humans.', "The symptoms known, respectively, as Creutzfeldt-Jakob disease and Alzheimer's disease are different manifestations of the same disease.", "Alzheimer's disease in rats is not caused by a virus."]