Factories, smoking, cars, littering
Onychomycosis/ a nail fungus... hope it helps :)
It is a good idea because it helps to detect if there is too much carbon monoxide in the house. If there is too much, it can be poisonous and the detector will let you know. this answer would be TO AVOID POISONING BY A BUILDUP OF CO GAS.
btw, is this platoweb? just curious.
It would be the third option going to support groups
