List two ways humans affect air quality

Tobacco Smoke

and

Combustion from Industry.~ Almost all of the common air pollutants can be produced by industrial processes.

hope i helped :]

i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.