The correct option is
B Genes
The human leukocyte antigen (HLA) system or complex is a gene complex encoding the major histocompatibility complex (MHC) proteins in humans. These cell-surface proteins are responsible for the regulation of the immune system in humans.HLA is the major cause of organ transplant rejections. Mutations in HLA may be linked to autoimmune disease. Hence, HLA is a group of genes.
So, the correct answer is 'Genes'.