This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Intravenous Anesthetic Agents, Subject name: Anaesthesia
Which of the following is Non - opioid intravenous anaesthetic agent? 
Select and explain. 
A. Tramadol, B. Pethidine, C. Fentanyl, D. Ketamine
D: Ketamine
Answer: D: Ketamine 
Explanation: Intravenous anaesthetic agents divided into two group- Opioids Non opioids Morphine Barbiturates Fentanyl Benzodiazepine Sufentanyl Ketamine Tramadol Etomidate and propofol The most potent opioid issufentanil