Answer: A. A sustainable energy source is one that will not run out.
Explanation: Sustainable energy sources are those that do not depend on the amount of natural resources, that is, they will not disappear, and they belong into desirable sources, especially nowadays. This includes wind energy, solar energy, geothermal energy, hydropower, biomass energy, and is desirable due to increasing pollution, ozone depletion and climate change arising from the use of fossil fuels.