It is an essential nutrient involved in the repair of tissue and the enzymatic production of certain neurotransmitters. Hence, the ascorbic acid is a $vitamin.$ $B$.Hormone - special chemical messengers in the body that are created in the endocrine glands. These messengers control most major bodily functions. C.Enzymes - proteins concerned in the catalysation of biochemical reactions. $D.Amino\,acid$ - bio micromolecues contains an amino group, $R$ group, $CooH$ group and $H$.So, the correct option is '$vitamin$'.