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: Dental
[{'content': "All of the following are true about vitiligo except: \nSelect and explain. \nA. Autoimmune destruction of melanocytes, B. Vitiligo vulgaris is the most common type, C. Black hair is a poor prognostic sign, D. Koebner's phenomenon positive", 'role': 'user'}, {'content': 'Answer: C \nExplanation: Since black hair follicle has melanocyte\xa0precursors, it is a good prognostic sign.', 'role': 'assistant'}]