Propane is a gas used in gas grills to cook food. During this process, the propane molecules undergo combustion with oxygen molecules to produce water and carbon dioxide, and a large amount of heat is released. Which statement best describes this process?

a. Heat is absorbed during this process as propane and oxygen molecules combust to make products.
b. Heat is released during this process as more carbon dioxide and water molecules are being produced.
c. Heat remains the same as the combustion process proceeds.
d. Heat is absorbed during this process as more carbon dioxide and water molecules are being produced.