The correct answer is D. Firewood.
Coal, petroleum, and natural gas are all commercial sources of energy. They are extracted from the Earth and used to generate electricity, power vehicles, and heat homes and businesses. Firewood is not a commercial source of energy. It is a renewable resource that can be harvested from forests, but it is not as efficient or cost-effective as other sources of energy.
Coal is a fossil fuel that is formed from the remains of ancient plants and animals. It is a solid fuel that is burned to generate electricity. Coal is the most abundant fossil fuel in the world, and it is the second-largest source of energy in the United States.
Petroleum is a fossil fuel that is formed from the remains of ancient marine organisms. It is a liquid fuel that is used to power vehicles and generate electricity. Petroleum is the largest source of energy in the world.
Natural gas is a fossil fuel that is formed from the remains of ancient plants and animals. It is a gas that is used to power vehicles, generate electricity, and heat homes and businesses. Natural gas is the third-largest source of energy in the United States.
Firewood is a renewable resource that is harvested from forests. It is a solid fuel that is burned to generate heat. Firewood is not as efficient or cost-effective as other sources of energy, and it can contribute to air pollution.