13. All of the wastes that people produce cause air pollution.F
14. Soil participles are natural pollutants.T
15. Polluted air has a harmful influence on people, plants and animals.T
16. Air pollution has become a serious problem due to the increasing population and industry.F
17.The word “they” in line 5 refers to:
B. natural pollutants
18. What does not contribute to air pollution?
D. the natural existence of oxygen in the air.