The function of somatic hypermutation is best described by which of the following statements?

A. increasing junctional diversity in IgH and IgL V regions

B. increasing the affinity of immunoglobulins for their antigen

C. irreversibly changing the isotype of immunoglobulin

D. promoting alternative splicing of an immunoglobulin heavy chain transcript to produce different isotypes on the B-cell surface

E. all of the above