Read the following paragraph and answer the question. Give ONLY the answer, no other words or explanation.

For example:

Answer: <most likely answer, as short as possible>.

Paragraph: 
Many of the problems with fossil fuels are worse for coal than for oil or natural gas. Burning coal releases more carbon dioxide than either oil or natural gas. Yet coal is the most common fossil fuel, so we continue to burn large amounts of it. That makes coal the biggest contributor to global warming.


Question: What is the most common fossil fuel?
coal
Coal.