The correct answer is D.
Sustainable energy is energy that will never be used or depleted, in other words, it's energy that is inexhaustible.
Sustainable energy is energy that meets the needs of present generations without compromising the needs of generations to come. It is about finding clean, renewable sources of energy, sources that renew themselves.
There are several forms of energy that can be renewable, such as wind, solar or water energy. There is also bio energy, which is energy created from biological masses such as straw and manure for example. Geothermal energy is another example, it is energy from Earth's internal sources, like geysers.
