One of the methods used to reduce energy use is:
a. energy efficiency
c. energy conservation
b. energy reservation
d. energy holding

Energy conservation.

Explanation:

The method to reduce the energy usage is known as energy conservation. This process reduces the loss of energy and helps in optimization of energy.

The energy can be wasted if it is not used in a proper way. Resources are meant to be used in such a way it fulfills the demand of current generation and future generations.

The best way to save energy for future is to conserve energy and use it in a optimum way.