pick from the following.
(a). Fuel cells
(b). using electricity
(c). animals
(d). Cooking
(e). organisms
(f). engines
(g). lightning
(h). solar power

Fact 1: Using a gasoline engine requires burning gasoline. Fact 2: Oil and gasoline are fossil fuels. Given the two facts above, what requires burning fossil fuels?
Answer:
(f).