Aman drink swamp water and later contracts malaria this fact alone does not provide conclusive evidence that swamp water is responsible for causing malaria to drive all conclusion with only needed

i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.