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: Anaesthesia
All are opioid agonist - antagonist compounds except – a) Buprenorphineb) Nalbuphinec) Pentazocined) Nalmefenee) Papaverine 
Select and explain. 
A. ab, B. bc, C. cd, D. de
D: de
Answer: D: de 
Explanation: Agonist antagonist opioids Pentazocine, Nalbuphine, Nalorphine, Butorphanol, Levallorphan, Dezocine, Meptazinol, Buprenorphine.