How Do Memory Cells Develop

How do memory cells develop?

A) Upon reinfection, memory centers in the brain send signals to the bone marrow to induce T-cell and B-cell differentiation.
B) T cells and B cells from the primary response persist and become reactivated.
C) Innate cells are trained to activate new T cells and B cells more quickly with secondary infection.
D) T cells and B cells from the primary infection slowly mutate their receptors over time, priming themselves for the secondary response.
E) Innate cells modify their cell surface receptors to prepare for reinfection.