This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
A patient is found to have sun-sensitive dermatitis, diarrhea, and dementia he must be suffering from the deficiency of which of the following. 
Select and explain. 
A. Niacin, B. Riboflavin, C. Folic acid, D. Iron
A: Niacin
Answer: A: Niacin 
Explanation: The most common symptoms of niacin deficiency involve the skin, the digestive system, and the nervous system. The symptoms of pellagra are commonly referred to as the three "Ds": sun-sensitive dermatitis, diarrhea, and dementia. A fourth "D," death, occurs if pellagra is left untreated