The correct option is C It uses the temperature difference in the ocean to generate energy.
OTEC is a non-conventional form of energy. The energy from the sun heats the surface water of the ocean. In tropical regions, the surface water can be 40 degrees warmer than the deep water. The Ocean Thermal Energy Conversion (OTEC) technologies utilize this temperature difference between the warm surface water of the oceans and cold water at a depth of approximately 1000 meters to drive power plants for electricity.
It is believed that OTEC is potentially capable of producing more energy than conventional tidal, wave, and wind energy combined. It does not produce any kind of pollution and is renewable in nature and neither does it cause any harm to life in the ocean.