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
Nitrous oxide is contraindicated in 
Select and explain. 
A. COPD, B. Asthma, C. Sickle cell anemia, D. All the above
D: All the above
Answer: D: All the above 
Explanation: None