Thedesertsoftheworldarenotallcoveredwithsand.Manyofthem...
問題詳情：Thedesertsoftheworldarenotallcoveredwithsand.Manyofthemhavesurfacesofrockorclayorsmallstones.Theyarenotflat,either.Theyoftenhavehighhillsanddeepvalleys.Thereissomeplants’lifeinmanypartsofthed...