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
Black tongue and black teeth are seen in abuse of 
Select and explain. 
A. Cocaine, B. Cannabis, C. LSD, D. Heroin
A: Cocaine
Answer: A: Cocaine 
Explanation: - 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