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: Medicine
A 35-year-old alcoholic presents with diarrhoea and scaly rash on his neck, hands and feet. He will improve if he is treated with which one of the following? 
Select and explain. 
A. Vitamin A, B. Thiamine, C. Folic acid, D. Nicotinic acid
D: Nicotinic acid
Answer: D: Nicotinic acid 
Explanation: None