In response to viral infection, the immune systems of mice typically produce antibodies that destroy the virus by binding to proteins on its surface. Mice infected with a herpesvirus generally develop keratitis, a degenerative disease affecting part of the eye. Since proteins on the surface of cells in this part of the eye closely resemble those on the herpesvirus surface, scientists hypothesize that these cases of keratitis are caused by antibodies to herpesvirus. Which of the following, if true, gives the greatest additional support to the scientists' hypothesis? ['Mice that have never been infected with a herpesvirus can sometimes develop keratitis.', 'Mice that are infected with a herpesvirus but do not develop keratitis produce as many antibodies as infected mice that do develop keratitis.', 'Other types of virus have surface proteins that closely resemble proteins found in various organs of mice.', 'There are mice that are unable to form antibodies in response to herpes infections, and these mice survive these infections without ever developing keratitis.']