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.