This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Drug Abuse, Subject name: Forensic Medicine
[{'content': 'Black tongue and black teeth are seen in abuse of \nSelect and explain. \nA. Cocaine, B. Cannabis, C. LSD, D. Heroin', 'role': 'user'}, {'content': 'Answer: A \nExplanation: - Black tongue and black teeth are seen in abuse of cocaine - Habitual inhalation of cocaine or heroin (snoing or sniffing) cause perforation of the nasal septum - Froth may be seen at the mouth and nose', 'role': 'assistant'}]