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
Stages of anaesthesia were established by – 
Select and explain. 
A. Ether, B. N2O, C. Halothane, D. Chloroform
A: Ether
Answer: A: Ether 
Explanation: Stages of anaesthesia were described by Guedel for ether.