This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nutrition, Subject name: Medicine
Deficiency of which one of the following dietary components is most likely to have caused this rash? 
Select and explain. 
A. Biotin, B. Folate, C. Niacin, D. Riboflavin
C: Niacin
Answer: C: Niacin 
Explanation: Answer C. NiacinThe symmetric, scaly, sunburn-like, hyperpigmented rash extending from the hands to a clearly demarcated border midway up the arm suggests a photosensitive distribution, most consistent with pellagra (niacin deficiency). Deficiency of the other listed dietary components is not typically associated with a photosensitive dermatitis in this area.