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: Psychiatry
Drug of choice for substitution therapy in morphine dependence- 
Select and explain. 
A. Methadone, B. Clonidine, C. Naloxone, D. Nalmefene
A: Methadone
Answer: A: Methadone 
Explanation: Ans. is 'a' i.e., Methadone