They are called hydrocarbons and are the basis of many organic compounds, including fuels.

Here's why:

* Hydrocarbons: This is the specific name for molecules composed only of carbon and hydrogen.

* Organic Compounds: The vast majority of organic compounds (those found in living things) contain carbon and hydrogen as their primary components.

* Fuels: Many hydrocarbons, like methane (CH4) and propane (C3H8), are used as fuels due to their energy-rich bonds.

Let me know if you'd like to know more about hydrocarbons or organic compounds!