Answer: Oil
Explanation:
In the graph you can see that the bottom line corresponds to the emissions of the natural gas, the second line corresponds to the coal, and the top line corresponds to the emissions of the oil.
You can see that the emissions of the oil are always bigger than the other two, and never intersects them (it is always above the 2000 line). From this, we can know that the fossil fuel that released the biggest amount of carbon dioxide each year is the oil
