Answer: a. geothermal
Step-by-step explanation:
The geothermal energy is the energy that is produced and stored in the geosphere of earth. The energy is generated in the form of hot water that liberates from the hot springs. The heat energy is generated in the mantle of the earth. The hot magma released from the mantle heat up the groundwater. Thus the water liberated is hot. This source of energy is used to heat up the buildings during winters, used in water bath and for other uses. This source of energy does not produce any form of waste like other conventional sources like biomass, nuclear and coal. Hence, waste disposal is not required in the case of geothermal energy.