Which of the following statements about hydrocarbons is true?

Hydrocarbons are organic compounds composed solely of carbon and hydrogen atoms. This unique composition is what defines them as hydrocarbons. This structure allows for a wide variety of configurations, including straight-chain, branched, and cyclic forms. The simplicity of their structure enables them to serve as fundamental building blocks in organic chemistry, leading to more complex molecules.

The other statements do not accurately describe hydrocarbons. For instance, hydrocarbons are generally hydrophobic, meaning they do not dissolve easily in water due to their nonpolar nature. While hydrocarbons are essential in many biological molecules, they do not occur as standalone entities in every living organism, as many biological structures also contain oxygen, nitrogen, and other elements. Additionally, the definition of hydrocarbons excludes the presence of other elements, as their defining characteristic is made up of only carbon and hydrogen.