Coal consists of nearly pure carbon, an element. When coal burns in air, it combines with the element oxygen from the air. Which of the following best describes the product of burning coal?

A. water, a heterogeneous mixture of atoms of hydrogen and oxygen
B. carbon dioxide, a heterogeneous mixture of atoms of carbon and oxygen
C. carbon dioxide, a homogeneous mixture of atoms of carbon gas and oxygen gas
D. carbon dioxide, a compound of atoms of carbon and oxygen