EricaDavidlivesinPinedale，Wyoming，USA，wherewintercanbringtemperaturesofbelow35degreesFahrenheit，howlingwinds，andalotofsnow．Soitwasjustnaturalthatshechosetostudysnowforherschoolsciencefairinthesixthgrade．

Nowajuniorinhighschool，Ericaisinhersixthyearofsnowexperiments，andiswellonherwaytobecomingasnowexpert．Shestartedwithabasicquestion：Couldsnowfencesbebuilttoworkbetter？

Snowfencesareusedtokeepsnowdrifts（雪堆）fromcoveringareaslikeroadsoftraintracks，ortohelpbuildupsnowwhereitcanhelpwithwatershortagesinspringwhenitmelts（融化）．"Also，Iwantedtoprotectmyanimalsbetterfromblowingsnow，"saysErica，whoraisesgoats，sheep，andpigs．

Beforeshecouldtestfencedesigns，Ericahadtofigureoutwhatwouldactlikerealsnowinherexperiments．"Itestedflour，sugar，andsaltbeforeIsettledondishwasherpowder，"sheexplains．

Sciencefairsofferstudentsthechancetotesttheories，presentfindingstojudges，andmeetotherresearchers．Erica'smanyachievementsincludecompetingattheDiscoveryChannelYoungScientistChallengeformiddleschoolstudentsandtheIntelInternationalScienceandEngineeringFair，wherestudentsfromaroundtheworldpresenttheirscienceresearch．

Butperhapsthebestrewardisthatherresearchisalreadybeingputtogooduse．Shehascomeupwithanimprovedsnowfencedesign，andthisyearshe'shelpingthinkouthowtoprovidewatersupplytonativeplants，whichhavebeenkilledoffbydrillingatnearbynaturalgasfields．

"Sciencefairsareanamazingexperience，"saysErica．"Justpickyourtruefeelingandgoforit．"

72．Whatdoesthepassagesuggesttous？___

A．SciencefairsareheldforhighschoolstudentsinAmerica．

B．EricaistheyoungestshowexpertwellknowninAmerica．

C．TheenvironmentbroughtmuchconvenienceforEricatostudysnow．

D．ThehopetocontributetoherhometownmadeEricaexperimentonsnow．

73．InErica'shometown，snowfencesmayplayapartin___．

a．reducingtheharmblowingsnowdoestoanimals

b．supplyingwaterresourcetothenearbygasfields

c．makingu