What are hydrocarbons primarily composed of?

Hydrocarbons are organic compounds that consist exclusively of carbon and hydrogen atoms. This means that their molecular structures are built entirely from these two elements. The simplest hydrocarbons, like methane (CH4), contain one carbon atom bonded to four hydrogen atoms. More complex hydrocarbons can have long chains or rings of carbon atoms, and the hydrogen atoms are bonded to these carbon structures.

The other options include additional elements like oxygen or nitrogen, which do not belong to the definition of hydrocarbons. For instance, alcohols and carboxylic acids, which contain oxygen in their structures, would not qualify as hydrocarbons. Therefore, stating that hydrocarbons are primarily composed of carbon and hydrogen is the defining characteristic that makes option C the correct answer.