The Number of Major Histocompatibility Complex (MHC)protein Combinations Possible in a Given

The number of major histocompatibility complex (MHC) protein combinations possible in a given population is enormous.However,an individual in that diverse population has a far more limited array of MHC molecules because

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