This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Environment and health, 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: Indoor air pollution originates from both outdoor and indoor sources, is likely to contribute to population exposure than the outdoor environment. The indoor environment represents an impoant microenvironment in which people spend a large pa of the time. Carbon monoxide, an indoor pollutant source include fuel/tobacco combustion. Combustion equipment, stoves, gas heaters all act as a source of carbon monoxide. Park's Textbook of Preventive and Social Medicine, 25th edition, Page No. 796