Which statement best describes the difference between responses of effector B cells (plasma cells) and those of cytotoxic T cells? a. B cells confer active immunity; cytotoxic T cells confer passive immunity. b. B cells respond the first time a pathogen is present; cytotoxic T cells respond subsequent times. c. B cells secrete antibodies against a pathogen; cytotoxic T cells kill pathogen-infected host cells. d. B cells carry out the cell-mediated response; cytotoxic T cells carry out the humoral response.