Select all statements correctly defining a hydrocarbon, and explain why alkanes are classified as saturated hydrocarbons:
I. A hydrocarbon is a compound consisting solely of carbon and hydrogen atoms.
II. Saturated hydrocarbons contain one or more double bonds between carbon atoms.
III. Alkanes are called saturated hydrocarbons because they contain only single bonds between carbon atoms and are fully saturated with hydrogen atoms.
IV. A hydrocarbon is a compound that contains carbon atoms bonded to hydrogen atoms and may include other elements such as oxygen or nitrogen.
V. Saturated hydrocarbons are characterized by having the maximum number of hydrogen atoms per carbon atom, with no double or triple bonds.