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: Pathology
[{'content': 'Magenta tongue is found in the deficiency of the vitamin \nSelect and explain. \nA. Riboflavin, B. thiamine, C. nicotinic acid, D. pyridoxine', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]