This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Inhalational Anesthetic Agents, Subject name: Anaesthesia
Stages of anaesthesia was described by:- 
Select and explain. 
A. WTG Moon, B. Oliver wendel homes, C. John snow, D. Guedel
D: Guedel
Answer: D: Guedel 
Explanation: None