a. Midwest has few sources of acid rain-forming pollutants.
Explanation:
Midwest has few sources of acid rain-forming pollutants because Midwest has less number of factories which produces less pollution. Farming, mining, and manufacturing of different products are the major industries Midwest. Other industries like transportation, finance, and machinery are also important for the economy of Midwest. Due to less number of factories less amount of pollutants goes to the atmosphere and will not cause acid rain.
