Question

Which of these buildings is most likely to have indoor air pollution?

a school with leaks that allow water and heat to be wasted
an office building without a carbon monoxide detector
a tightly sealed house with an unvented water heater

Answer 1

when heater is on for long time without having ventilation then carbondioxide will be converted into carbon monoxide and causes air pollution.

So according to above explanation,

C. A tightly sealed house with an unvented water heater, is the correct answer

Answer 2

the one with the highest likelihood of air pollution is a tightly sealed house and might have an invented water heater
hope i helped (: