The correct answer is (a) evaporation control
To explain: The following are some of the methods of evaporation control such as Windbreakers, Reduction in the exposed water surface, Use of underground storage rather than surface storage, Integrated operation of reservoirs, and Use of chemical for retarding the evaporation rate from the reservoir surface. Use of Water Evapo-Retardants (WERs) is considered to be an only practical solution for the conservation of freshwater in spite of its limitations and disadvantages.