The correct answers are "coal", "petroleum", "fuel cells" and "oil".
Explanation:
The energy solutions that release pollution into the air are coal, petroleum, fuel cells and oil. Coal was one of the first sources of energy to be used in the industry, the smoke generated from coal power plants is extremely dangerous and pollutant. Petroleum and its by products are very contaminant as well, producing high amount of carbon dioxide emissions as well as other greenhouse gases. Fuel cells are much cleaner than the other energy solutions however they still produce contamination into the air, specifically one ounce of pollutant for every 1,000 kW·h produced. Oil is also a contaminant of air, particularly when oil spills take place which are producers of carcinogens and aerosols.
