The presence of harmful substances in the air is called / the answer here/ . polluted air indoors or outdoors can be /the answer here/ to a person’s health, and can have many negative environmental effects. air pollution can also lead to
/the answer here/

beneficial, climate change, air erosion, air pollution, hazardous, oxygen /these are the answers to pick out of from/

Indoor pollution can be reduced by reducing the main causes of this pollution which are: avoid smoking indoor, reducing use of carpeted floors, proper ventilation,    keep trash baskets covered, minimizing the use of air-fresheners and irritating perfumes, use exhaust fans. The outdoor pollution can be reduced by minimizing the use of vehicles whose burning fuel contribute a lot to outdoor air pollution, the chimneys of industries and factories should have filters fixed in so that harmful substances may not be exposed to air.

positive reinforcement? ?

a and b sometimes have a positive value