Although the Number of Major Histocompatibility MHC) Protein Isoforms Possible

Multiple Choice

Although the number of major histocompatibility MHC) protein isoforms possible in a given human population is enormous, why does each individual have a limited array of MHC molecules?

A) because once a B cell has matured in the bone marrow, it is limited to two MHC response categories
B) because each of the MHC genes has a large number of alleles, but each individual inherits only two for each gene
C) because once a T cell has matured in the thymus, it can only respond to two MHC categories
D) because the MHC proteins are made from several different gene regions that are capable of rearranging in a number of ways
E) because the MHC proteins from one individual can only be of class I or class II