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Unit1ProjectProducingaTVshowSharkattacks•SharkSpeciesWhalesharkBullsharkGreatwhiteTigershark•OthersharkfactsSharkshavefivetosevengillslits(鳃裂).Manysharksmustkeepmovinginordertobreathethatis,inordertokeepwatermovingpasttheirgillslitsbutthisisnottrueofallspecies.Nursesharks,forexample,canliestillandfantheirgillstobringoxygen-richwateracrosstheslits.Becausetheylackaswimbladder(气囊),allsharksmustswiminordertoavoidsinkingtowardtheoceanfloor.•Thesharkhassensesspeciallyadaptedfortheanimal'slifeunderwater.Smellisashark'smostacutesense.Approximately70percentoftheshark'sbrainisusedforsmellingfunctions.Experimentshaveshownthatsharkscandetectanimalsbysmell.•Sharksaresensitivetolightandcandetectcertainobjectseveninmuddywater.Somehaveamirror-likelayerundertheretina(视网膜)oftheeyethatreflectsincominglightandincreasestheamountoflightavailabletotheeye.(Catsandotheranimalswhoseeyesglowinthedarkalsohavethisfeature.)•Sharkscanalsosenseelectricandmagneticfields.Sensoryporeslocatedontheshark‘sheadcandetectaprey’sbioelectricfieldevenifthepreyisburiedinsand.AsharkcanalsodetecttheEarth‘smagneticfield.Open-oceansharksmayusethisinformationtonavigate(导航)andorient(定位)themselves.Sharkwaterisa2006CanadiandocumentaryfilmwrittenanddirectedbyRobStewart,whoalsonarratesit.Inthefilm,Stewartseekstodeflatecurrentattitudesaboutsharks,andexposeshowthevoracious(贪吃的,胃口极大的)shark-huntingindustryisdrivingthemtoextinction.DocumentReadingformainidea:Para.1Therearenearly400typesofsharks,andsomewell-knowntypesofsharksthatattackhumans.Para.2ThreetypesofsharkattacksPara.3FourtipsonhowtoavoidbeingattackedPara.4Anincreaseinwatersportshasledtoanincreaseinsharkattacks.Threetipsonwhattodoifasharkattacks.Para.5:Donotbefrightenedbysharks.ThewonderfulworldofpigeonFromancienttimes,pigeons—especiallyhomingpigeons,whicharealsousedasracingbirds—havebeenusedforcarryingmessages.Althoughelectronicshaslargelyreplacedthemasmessengers,theyarestillofexperimentalimportance.Readingforquestions:1.Whatdoesthearticlebeginwith?2.Whatisthestoryabout?3.Whydoesthewriterbeginwiththisstoryinhisarticle?4.Whydopigeonsnevergetlost?