Which Statement About Immunoglobulins Is True

Which statement about immunoglobulins is true?

A) Immunoglobulin chains have domains, each of which is encoded by one of a number of possible genes selected from a set of similar genes.
B) Each mature B cell makes several different antibodies that target different antigens.
C) The heavy chains of mouse immunoglobulins have two domains, one in the variable region and one in the constant region.
D) A single gene encodes each immunoglobulin.
E) The supergene that codes for the heavy chain of an immunoglobulin molecule is the same in most B cells.