Question

which of the following is one of the four most dangerous indoor air pollutants as identified by the epa?
hydrogen
oxygen
tobacco smoke
nitrogen

Explanation:

Hydrogen, oxygen, and nitrogen are common, non - polluting (or minimally polluting in normal indoor contexts) gases. Tobacco smoke contains numerous harmful chemicals (like carcinogens) and is identified by the EPA as one of the four most dangerous indoor air pollutants.

Answer:

C. tobacco smoke (assuming the options are labeled A: hydrogen, B: oxygen, C: tobacco smoke, D: nitrogen)