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
Which of the following is an indor air-pollutonts- 
Select and explain. 
A. Carbon dioxide, B. HCN, C. Methan, D. Perfluoro carbons
A: Carbon dioxide
Answer: A: Carbon dioxide 
Explanation: Ans. is 'a' i.e., Carbon dioxide Important indoor air pollutantsPOLLUTANTSSOURCESRespirable particlesTobacco smoke, Stove, Aerosol sprays.Carbon monoxideCombustion equipment, Stove, Gas heaters.Nitrogen dioxideGas cookersCigarettesSulphur dioxideCoal combustionCarbon dioxideCombustion, respirationFormaldehydeParticle board, Carpet adhesives, Insulation.Other organic vapours(benzene, toluene, etc)Solvents, adhesives, resin products, aerosol sprays.OzoneElectric arcing, UV light sourceRadon and "daughters"Building materialAsbestosInsulation, Fire proofingMineral fibersAppliances