Answer:
Natural Gas
Step-by-step explanation:
It is when fossil fuels like coal and other natural gasses are burned that greenhouse gas is emitted. Nuclear power does hold some danger if left unchecked, but does not contribute to greenhouse gasses in a significant way. Hydroelectric energy does not produce any greenhouse gasses as well. Geothermal energy is also something that does not produce greenhouse gasses and is renewable. The main reason why natural gasses are still used although they produce large numbers of dangerous gasses is because they cost much less than the other energy sources on this list.