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
In Indoor air pollution, carbon monoxide is produced by- 
Select and explain. 
A. Combustion equipment, B. Stove, C. Gas heaters, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: Ans. is 'd' i.e., All of the above Pollutant Sources Carbon monoxide Combustion equipment,stove, Gas heater. Nitrogen dioxide Gas cookers, Cigarattes Sulphur dioxide Coal combustion Carbone dioxide Combustion, respiration Ozone Electric arcing, UV light sources