関連ワード:  sources of air pollution class 12th    causes of air pollution class 12    causes of environmental pollution class 12    describe the major sources of air pollution class 12    mention two main sources of air pollution class 12    mention two main sources of air pollution class 12 geography    describe the major sources of air pollution class 12 geography    write major causes of air pollution class 12    discuss the causes of environmental pollution class 12 political science    mention four causes of environmental pollution class 12