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: Pharmacology
Hallucination is the major side effect of : 
Select and explain. 
A. Nitrous oxide., B. Ketamine, C. Fentanyl, D. Chloroform
B: Ketamine
Answer: B: Ketamine 
Explanation: None