The number of 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.