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: Pharmacology
The most important feature of the following opioid analgesic is high oral parenteral activity ratio (1:2): 
Select and explain. 
A. Morphine, B. Oxymorphine, C. Methadone, D. Diacetylmorphine
C: Methadone
Answer: C: Methadone 
Explanation: None