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
Acanthosis nigricans is caused by which drug - 
Select and explain. 
A. Amphotericin-B, B. Ketoconazole, C. Nicotinic acid, D. Nalidixil acid
C: Nicotinic acid
Answer: C: Nicotinic acid 
Explanation: None