Ais a mound of sand that is created by the wind and usually is formed on sea coasts or in deserts. a. hill b. silt c. dune d. loess

  C. Dune

Explanation:  Dune is a typical form of relief of the desert and sandy sea coasts. It represents a hill formed from loose sand, under the influence of  aeolian processes-wind or the flow of water.  It does not represent a permanent form of relief, and therefore should not be considered as a reliable orientation, especially in the desert. After each wind, the dune can change shape and place.