【由北京市丰台区2014高考模拟改编】阅读下列短文，从每题所给的A、B、C、D四个选项中，选出最佳选项。Haveyoueverlookedtowardtheskyonafalldayandwitnessedagroupofmigratingbirds?Ifso,youprobablynotedtheV-shapedformationofthebirdsorthebirdsflyinginaball-likeformation.Whydobirdsflythisway?Manytheorieshavebeendevelopedtoexplaintheformationpatternsofdifferenttypesofbirds.Onetheoryisthatbirdsflyincertainformationstotakeadvantageofthelawsofnature.ThebirdsknowthatflyinginaV-shapedpatternwillsaveenergy.Liketheleadcyclistinaracewhodecreaseswindforceforthecyclistswhofollow,theleadbirdcutswindforceforthebirdsthatfollow.Thisdecreaseinwindforcemeansthatthebirdsuseupto70percentlessenergyduringtheirflight.Whentheleadbirdbecomestired,amorerestedbirdtakesoverthatposition.Butsavingenergyisimportantformorethanonereason.Sometimesfoodisshortduringmigrationflights.Keepingenergyenablesthebirdstoflylongerdistancesbetweenmeals.Whenfoodissighted,thebirdsguideoneanotherinadifferentway.Whenabirdidentifiesafamiliarfeedingarea,itmightturnaroundinordertosignalthegrouptochangedirection.Then,thisbirdbecomesthenewleader.Ithelpsguaranteethatotherbirdswillknowexactlywhereitisgoing.Thenthewholegroupmakesachangeindirection,gentlystreamingfromtheskydowntotheground.Thisformationislikeanarrowpointingtothelocationoffood.Scientistshavealsostudiedthebirdsthatsometimesflyinaball-likeformation.Researchersbelievethatthebirdscometogetherifapredator（天敌）isspotted.Thepredatormaythenbecomeimpatientwaitingforasinglebirdtoflyawayfromthegroup.Thebirdswilloftendipanddiveasagroup,frustratingeventhemostpersistentenemy.Scientistsreportthatthisisaveryeffectivemethodofdefenseagainstanattack.Thebirdscarefortheirfellowfliersthroughteamwork.AstransportationexpertHenryFordoncesaid,“Ifeveryoneismovingforwardtogether,thensuccesstakescareofitself.”Whenitcomestoteamwork,thesefeatheredfliersareasoaringsuccess!1.Accordingtothepassage,wecanlearnthatbirds___________.A.movefasterthancyclistsB.prefertoflyinaVformationC.aresmarterthanotheranimalsD.playdifferentrolesinaformation