Which of the following is NOT listed as an alternative vehicle fuel source?

Electricity is often classified as an alternative fuel source; however, within the context of vehicles specifically designed to run on different fuels, it may not always be included in the same category as propane, natural gas, and jet propellant. Alternative vehicle fuel sources typically refer to non-conventional fuels that are used to power vehicles, which may include propane, natural gas, and certain types of synthetics or biofuels. These fuels are classified as alternatives because they serve as substitutes for traditional gasoline or diesel. Jet propellant, while commonly used in aviation, is also off the standard list of alternative fuels for ground vehicles.

The distinction here is that while all of these fuels can power vehicles, electricity tends to represent a broader energy source for various applications, often associated with electric vehicles that utilize batteries and charging systems rather than being a fuel source in the same way as the others listed. Therefore, electricity can be seen as a less conventional choice when strictly considering fuels in the context of vehicle operation compared to the others listed.