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: Skin
[{'content': 'A 17 year old girl with acne has been taking a drug for the last two years. She now presents with blue black pigmentation of nails. The likely medication causing the above pigmentation is: \nSelect and explain. \nA. Tetracycline, B. Minocycline, C. Doxycycline, D. Azithromycin', 'role': 'user'}, {'content': "Answer: B \nExplanation: There may be diffuse blue-gray, muddy appearance in sun exposed areas and hyperpigmentation of mucous membranes, teeth, nails, bones and thyroid in patients taking minocycline for longer duration. Ref: Skin Diseases and Sexually Transmitted Infection, Uday Khopkar, 6th Edition, Page 110; Handbook of Dermatologic Drug Therapy By Steven R. Feldman, Kathy C. Phelps, Kelly Campbell Verzino, Page 42; Harrison's Principles of Internal Medicine, 16th Edition, Pages 303, 1229.", 'role': 'assistant'}]