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
Which one of the following is the shoest acting intravenous analgesic: 
Select and explain. 
A. Remifantanil, B. Fentanyl, C. Alfentanil, D. Sufentanil
A: Remifantanil
Answer: A: Remifantanil 
Explanation: A i.e. Remifentanil