<prompt> Rheumatoid factors are immunoglobulins directed against:The Fc poion of immunoglobulin G IgGThe Fc poion of immunoglobulin A IgAThe Fc poion of immunoglobulin M IgMThe Fc poion of immunoglobulin D IgD  <response>: The Fc poion of immunoglobulin G IgG 