ATrainFloatingOnAir 　　Atrainthatfloatsonair?It'snotmagic—it'smagnets（磁）．Andit'sclosetoreality． 　　InVirginiaUSAthefallof2002,atrainwithnowheelstraveledonairandcarriedcollegestudentsacrosstheircampus．InJapan,awhisper-quietrailwayenginehoveredandracedat350milesperhourusingmagnetsandelectricityasthepower．AndinChina,amagnettrainlinelinkedShanghaiwithnearbyPudongAirport． 　　Thesetrainsusemagneticlevitation（悬浮）technology,"maglev"forshort．Theyusethesamerulesasthemagnetsyoupickupathomeorschool:oppositepolesofmagnetsattracteachother,andlikepolesrepeleachother． 　　Howdoesitwork? 　　Powerfulmagnetsonthebottomofthetrainrepelmagnetsonthetrack,whichisactuallyjustamagnet-filledguidingway.Withamagneticfieldofsufficientforce,thetrainwillgohoveringonair,whichseemedimpossibletousinthepast． 　　Whenanelectricalcurrentissentthroughthetrack,thetrainmoves．Turnthecurrentbackwardsandthetrainslowsdown． 　　Maglevdoesn'trelyonthefriction（摩擦力）ofwheelsontrack,soitcanclimbamuchsteeperhillthanatraditionaltrain．Anditcantraveleasilyinsnowandice,somethingthatcouldbringnormaltrainstoascreamingstop． 　　49．Thispassageisabout． 　　A．maglevB．magnetsC．levitationD．electricity 　　50．Whichofthefollowingisarepellingaction? 　　51．Whatcanwelearnfromthetext? 　　A．Amagnet-filledguidingwayisformedinsideamaglevtrain． 　　B．Insteadofelectricity,magnetsareusedasthepowerofamaglev． 　　C．Maglevtrainscanclimbhillswiththehelpofmagnetwheels． 　　D．Electriccurrentsdecidethemovementsofamaglevtrain． 　　52．Whatisthedifferencebetweenamaglevtrainandanordinarytrain? 　　A．.Amaglevtraincanclimbmountainswithoutpowerwhileanordinaryonecan't． 　　B．Amaglevtraincantravelincollegecampuswhileanordinarytrainisnotallowed． 　　C．Travellingwithoutatrack,amaglevtrainissaferandsmootherthananordinaryone． 　　D．Floatingonatrack,amaglevtrainisfaster,quieterthananordinaryrailwaytrain． 　　我帮你百度的,不知道是不是你想要的.