Answer:
Coal, Oil and Natural Gas.
Explanation:
Coal: It is the primary fuel for the production of electricity and is responsible for about 40% of the electric power supply in the United States. The burning of coal and the mining process is harmful to the environment releasing air pollutants such as sulfur dioxide, nitrogen oxide, and mercury.
2. Oil: Oil is the primary source for the world's transportation. Most oil is pumped out of underground reservoirs but may also be found in shale and tar sands.
3. Natural Gas: About 27% of U.S. energy is fueled by natural gas. It is commonly used to produce heat or electricity for buildings and industrial processes.
