The correct answer is C. both (A) and (B).
A multipurpose reservoir is a reservoir that is planned and constructed to serve various purposes, such as water supply, irrigation, flood control, and hydroelectric power generation.
Option A is incorrect because a multipurpose reservoir is not designed for one purpose but serves more than one purpose. It is planned and constructed to serve various purposes.
Option B is incorrect because a multipurpose reservoir is not just planned and constructed to serve various purposes. It is also designed for that purpose.
Option D is incorrect because a multipurpose reservoir is both designed and constructed to serve various purposes.