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
[{'content': 'Cheilosis may result from deficiency of all except : \nSelect and explain. \nA. Vitamin B12, B. Iron, C. Nicotinic acid, D. Riboflavin', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]