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
Route of administration of nitrous oxide is: 
Select and explain. 
A. Inhalation., B. Oral., C. Intramuscular., D. Intravenous.
A: Inhalation.
Answer: A: Inhalation. 
Explanation: None