Answer: The correct option is (a).
Explanation:
Windmills: In wind mill, the kinetic energy from the moving air is converted into electricity by wind turbines.
Wind energy is a renewable source of the energy. It is inexhaustible source of the energy.
Wind energy is used to sail ships.
It is unlimited. It is non polluting way to generate electricity.
The wind mills are mostly located in the coastal area. They are currently being used to provide energy.
But it is unreliable source of energy. If the wind blowing then the wind energy cannot be converted into electrical energy by using wind turbines in the case of windmills.
Wind is necessary to generate wind energy.
Therefore, the correct options (a).