In Cell Culture Experiments, Purified B Cells Expressing IgM Can

In cell culture experiments, purified B cells expressing IgM can be induced to switch to producing IgE by stimulating them with an antibody to CD40 (a stimulatory antibody) plus the cytokine IL-4. In an individual undergoing an immune response, these signals would normally be provided by:

A) Germinal center stromal cells
B) Other B cells in the germinal center
C) Follicular dendritic cells in the germinal center
D) Any CD4 T cell in the same lymph node
E) T_FH cells in the germinal center