Approximately about 25% of the Sahara Desert is covered by sand sheets and dunes. Therefore, correct option is B.
A dune is a mound of sand formed by the wind, usually along the beach or in a desert.
Dunes form when wind blows sand into a sheltered area behind an obstacle.
Dunes grow as grains of sand accumulate. Every dune has a windward side and a slip-face.
Therefore, correct option is B.
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