Differences in the B- cell receptors of two different B cells are due to

A) the rearrangement of C- region genes in that clone of responsive B cells.
B) a switch in the kind of antigen- presenting cell that is involved in the immune response.
C) a patient's reaction to the first kind of antibody made by the plasma cells.
D) the recombination of variable regions of the light- chain and heavy- chain genes.
E) mutation in the genes of that B cell, induced by exposure to the antigen.