Antibody Heavy and Light Chain Polypeptides Consist of Repeated Domains

Antibody heavy and light chain polypeptides consist of repeated domains, each of which is ~110 amino acids and folds up into a compact three-dimensional structure known as an 'immunoglobulin domain.' These immunoglobulin domains are:

A) Mixed and matched between different antibody heavy and light chains to produce variability
B) Always identical to each other within a single antibody heavy chain or light chain polypeptide
C) Always differ in amino acid sequence between different light chain polypeptides in both of the two light chain immunoglobulin domains
D) Similar but not identical in amino acid sequence when comparing the domains in a single heavy chain polypeptide
E) Identical in amino acid sequence for every domain when comparing different antibody heavy chain polypeptides to each other