Both A and C are correct. Both A and C are correct. The clonal selection theory implies that related people have similar immune responses. Antigens activate specific lymphocytes. Only certain cells can produce interferon.
Memory cells are present at birth.
The body selects which antigens it will respond to. Cell-mediated immunity is mostly the function of T cells. Which term best fits the process in which an attenuated pathogen is used to stimulate the body to produce antibodies against the pathogen clonal selection opsonization complement system passive immunity vaccination 50.