Concept:Perennial irrigation supplies water to farmland throughout the year, usually with the help of rivers, dams, and canals.Explanation:The Sudan experiences low and unreliable rainfall over much of its land.It relies heavily on the River Nile and its tributaries for farming.Large schemes such as the Gezira Scheme practice perennial irrigation to grow crops like cotton and sorghum all year round.None of the other listed countries depend as extensively on perennial irrigation as a major agricultural system.Answer:C. The Sudan