Aheart attack occurs when . a. a coronary vessel is completely plugged and the surrounding tissue dies b. gradual enlargement of a plaque narrows the blood vessel lumen c. a patient experiences angina pectoris d. blood flow is reduced to the legs e. enlarged atherosclerotic plaque ruptures

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.