Oneoftheworld'sgreatnaturalwondersisinNewMexicointhesouthwestofAmerica.Naturehascreatedhugemovinghillsofpurewhitesand.Thesesanddunescovermorethanseventy­thousandhectaresofdesert.Itisoneofth

　　Oneoftheworld'sgreatnaturalwondersisinNewMexicointhesouthwestofAmerica.Naturehascreatedhugemovinghillsofpurewhitesand.Thesesanddunescovermorethanseventy­thousandhectaresofdesert.

　　ItisoneofthelargestsanddunefieldsintheUnitedStates.Thebrightwhitesanddunesarealwayschanging，alwaysmovinglikewavesontheocean.Drivenbystrongwindsthesandmovesandcoverseverythinginitspath.Itislikeahugeseaofsand.

　　Youmaywonderhowanythingcanliveinthisextremeenvironmentofawhitesanddesert.Thereisnotmuchrain.Theheatinsummerisintense.Thesandlacksnutrients.Plantsandanimalsstruggletosurvive.Afewkindsofplantsgrowquicklytosurviveburialbythemovingsanddunes.Severalkindsofsmallanimalshavebecomewhiteincolorinordertohideinthesand.

　　MorethanfivehundredthousandpeoplevisitWhiteSandseachyear.Theyclimbonthedunesandobservethemovingseaofsand.

　　WhiteSandsisabouttwentyfourkilometerssoutheastofthecityofAlamogordoNewMexico.Inthevisitorcenterattheentranceoftheparkyoucanfindoutspecialactivitiesandguidedwalks.Youcandriveaboutthirteenkilometersintothecenterofthedunes.Itislikedrivingonalonelywhiteplanet.AlongthewaythereisinformationthattellsaboutthenaturalhistoryofWhiteSands.

　　Youcanalsoexplorethedunesonfootseeingsomeunusualandbeautifulplantsandflowers.Signsalongthetrailtellabouttheplantsgrowinginthesand.Youcanevencampthereovernight.Butyoumustbecareful.Itiseasytogetlostinthewavesofmovingsandespeciallyduringsandstorms.Thereisnowatertodrink.ThetemperaturecanrisetothirtyeightdegreesCelsiusinsummer.Thereisnoshelterfromthesun'srays.

　　WhiteSandsispartofAmerica'sNationalParksSystemanditisjustoneoftheunusualexamplesofAmerica'snaturalandculturaltreasures.

　　16．Whichofthefollowingplaysamajorroleinmakingfortheextremeenvironment?

　　A．Plantsandanimals.

　　B．Strongwinds.

　　C．Intenseheatandlittlerain.

　　D．Manypeople.

　　17．Walkingondunespeoplewill________．

　　A．enjoythebeautifulsightofsandmoving

　　B．seemanykindsofwhiteplantsandani