Biofuels are now being used worldwide and supporters claim that they are a sustainable, renewable and cleaner alternative to traditional fossil fuels such as coal and petroleum, supplies of which are becoming depleted. Biofuels are increasingly used in the transportation sector. The main producers of biofuels are in Asia, Europe and America. They can be produced from any carbon source including landfill gasses and recycled vegetable oil but most of the biofuel produced around the world is derived from photosynthetic plants grown in Brazil. The two main types of plant used in production are those high in sugar, which are fermented to produce ethanol, and those high in oil, which have the oil extracted and heated to reduce viscosity before the oil is used. Advocates explain that burning biofuels releases the same amount of CO2 that the plants took out of the environment during their growth so there is no net increase in levels of atmospheric carbon.

Question: Biofuels can be used to power aircraft.
Options:
A. true, B. false, C. uncertain
Answer: "C"