Your Sister-In-Law Never Gets Sick, While Her Male Neighbor Seems

Your sister-in-law never gets sick, while her male neighbor seems to be sick all the time. Although there are several possible explanations for this, one is that they are genetically different. Which of the following hypotheses concerning genetic inheritance of major histocompatibility complex (MHC) molecules is consistent with this observation and your understanding of the immune system?

A) Individuals who are homozygous dominant for MHC genes are healthier than those who are homozygous recessive for MHC genes.
B) In the case of MHC, it is beneficial to have as many different alleles as possible, so individuals heterozygous for the multiple MHC genes are healthier than those who are mainly homozygous for MHC genes.
C) MHC proteins are often closely associated with small antigen particles that have been broken off the main pathogen, so individuals who are recessive for MHC don't normally have many illnesses because they don't produce these MHC-antigen complexes.
D) Some individuals undergo greater levels of somatic hypermutation for the MHC genes.