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: Social & Preventive Medicine
Which one of the following is not a greenhouse gas ? 
Select and explain. 
A. Carbon monoxide, B. Methane, C. Nitrous oxide, D. Water vapour
A: Carbon monoxide
Answer: A: Carbon monoxide 
Explanation: None