This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: JIPMER 2019, Subject name: Anaesthesia
Which of the following induction agent causes least respiratory depression?. 
Select and explain. 
A. Midazolam, B. Ketamine, C. Propofol, D. Thiopentone
B: Ketamine
Answer: B: Ketamine 
Explanation: Ketamine maintains upper airway reflex and causes less depression of respiratory center compared to other agents