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: Dental
[{'content': 'N2O more than 30 — 40% causes \nSelect and explain. \nA. Diffusion hypoxia, B. Anoxia, C. Amnesia, D. Ataxia', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]