Which one of the following statements about humoral immune responses is true?

Which one of the following statements about humoral immune responses is true?
 
  A. Naive B cells are required for initiation of primary responses and memory B cells are required for initiation of secondary responses.
  B. Antibody responses to bacterial polysaccharide antigens require CD4+ helper T cells.
  C. Heavy chain isotype switching typically occurs in response to bacterial polysaccharide antigens.
  D. Affinity maturation does not require helper T cells.
  E. Antibody-secreting cells generated during a humoral immune response live for only a few hours.