The correct answer is B. Geothermal.
This is true because geo relates to the earth and thermal relates to heat.
When you put those two words together, it means heat from the earth.
A is incorrect since the energy sources comes from the fission or splitting of atoms.
C is incorrect since solar energy relates to heat or energy from the sun.
D is incorrect since hydro means water and therefore hydroelectricity is an energy source that is made from water.