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 described by Guedel with 
Select and explain. 
A. Ether, B. Chloroform, C. N20, D. Halothane
A: Ether
Answer: A: Ether 
Explanation: Ether