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': 'Acanthosis nigricans is caused by which drug - \nSelect and explain. \nA. Amphotericin-B, B. Ketoconazole, C. Nicotinic acid, D. Nalidixil acid', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]