The correct answer is 13 because there are 13 essential vitamins that are required for the proper functioning of the human body. These vitamins include vitamin A, B (thiamine, riboflavin, niacin, pantothenic acid, biotin, vitamin B6, vitamin B12, and folate), vitamin C, vitamin D, vitamin E, and vitamin K. These vitamins play a crucial role in various bodily functions such as metabolism, immune system support, bone health, and protection against oxidative stress.