Answer:
A. One that is not a fossil fuel
Step-by-step explanation:
"Alternative fuel" is a technical term used in the fuel industry. It refers to fuels that that are not fossil fuels (like coal, oil, and natural gas).
B. is wrong. A fuel that hasn't been developed yet is not of much use.
C. is wrong. A homeowner may consider wood as an alternative fuel in case there is no electricity to power an oil furnace, but that is not the technical meaning of the term.
D. is wrong. An alternative fuel should use renewable resources.