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 Everyone wants to reduce pollution. But the pollution  problem is verry  complicated  It's complicated because much pollution is caused by things that benefit people. For example, exhauxt from automobiles causes a large percentage of all air pollution. But the automobile provice  transportation for millions of people. Factories discharge  much of the material that pollutes air and water, but factories give employment to a large number of people. 
1 what things benefit people?
2 what can factories do for a large number of people ?