Which of the following indicates that the immune system has achieved versatility? A)Millions of NK cells are produced to ensure efficient immune surveillance. B)Lymphocytes, which are sensitive to an antigen, undergo repeated cell divisions. C)Production of many normal B cells and T cells, which will attack "self" antigens, occurs. D)Lymphocyte cell divisions produce two cell types: one group, which will attack specific antigens, and another group, which will remain inactive until exposed to the same antigen later. E)Millions of different lymphocyte populations are produced, each with different antigen receptors.