B

Scientistshavedevisedawaytodetermineroughlywhereapersonhaslivedusingastrand(缕)ofhair,atechniquethatcouldhelptrackthemovementsofcriminalsuspectsorunidentifiedmurdervictims.

Themethodreliesonmeasuringhowchemicalvariationsindrinkingwatershowupinpeople’shair.

“You’rewhatyoueatanddrink,andthat’srecordedinyourhair,”saidThureCeiling,ageologistattheUniversityofUtah.

WhileU.S.dietisrelativelyidentical,watersuppliesvary.Thedifferencesresultfromweatherpatterns.Thechemicalcompositionofrainfallchangesslightlyasraincloudsmove.

Mosthydrogenandoxygenatomsinwaterarestable,buttracesofbothelementsarealsopresentasheavierisotopes(同位素).Theheaviestrainfallsfirst.Asaresult,stormsthatformoverthePacificdeliverheavierwatertoCaliforniathantoUtah.

SimilarpatternsexistthroughouttheU.S.Bymeasuringtheproportionofheavierhydrogenandoxygenisotopesalongastrandofhair,scientistscanconstructageographictimeline.Eachinchofhaircorrespondstoabouttwomonths.

Cerling’steamcollectedtapwatersamplesfrom600citiesandconstructedamapoftheregionaldifferences.Theycheckedtheaccuracyofthemapbytesting200hairsamplescollectedfrom65barbershops.

Theywereabletoaccuratelyplacethehairsamplesinbroadregionsroughlycorrespondingtothemovementofrainsystems.

“It’snotgoodforpinpointing(精确定位),”Cedingsaid.“It’sgoodforeliminatingmanypossibilities.”

ToddPark,alocaldetective,saidthemethodhashelpedhimlearnmoreaboutanunidentifiedwomanwhoseskeletonwasfoundnearGreatSaltLake.

Thewomanwas5feettall.Policerecovered26bones,aT-shirtandseveralstrandsofhair.

WhenParkheardabouttheresearch,hegavethehairsamplestotheresearchers.Chemicaltestingshowedthatoverthetwoyearsbeforeherdeath,shemovedabouteverytwomonths.

ShestayedintheNorthwest,althoughthetestcouldnotbemorespecificthansomewherebetweeneasternOregonandwesternWyoming.

“It’sstillasubstantialarea,”Parksaid.“Butitnarrowsitwaydownforme.”

61.Accordingtothepassagescientists’newdiscoveryisthat &nbs