Why would my doc prescribe b1, B6 and B12 together?

Vitamin B-1, B-6 B12. Vitamins B-1, B-6 and B-12 each fill many different roles that support body’s metabolism, convert food into energy , help it produce essential substances, such as neurotransmitters, red blood cells and hemoglobin; and white blood cells that support the immune system. Discuss with Physician your health status, any Vitamin deficiency and these benefits.