Which of the following is a greenhouse gas produced when fossil fuels burn?

The combustion of fossil fuels (hydrocarbons) in the presence of oxygen releases energy along with chemical products. The primary greenhouse gas emitted during this process is Carbon dioxide (${\text{CO}}_2$).
$$\text{Hydrocarbon}+{\text{O}}_2\to {\text{CO}}_2+{\text{H}}_2\text{O}+\text{Energy}$$

While carbon monoxide ($\text{CO}$) is produced during incomplete combustion, it is not primarily classified as a major direct greenhouse gas like ${\text{CO}}_2$.