Concept:Drip irrigation is the most water-efficient method because it supplies water directly to the plant root zone.Explanation:In flood, furrow, and border irrigation, water is spread across or along the soil surface.These surface methods lose more water through evaporation, deep seepage, and runoff.Drip irrigation releases water slowly and precisely at the roots, so the plant absorbs almost all of the water.This greatly reduces wastage and conserves water better than the other options.Answer:D. drip irrigation