Reading-strategy-skimming

ReadingStrategySkimmingSkimmingisusefulinourlifeandstudy.Skimmingmeansreadingquicklyforthemainideasofatext.Whatisskimming?Tip1Readthetitleandsubtitle.SharksSharksareamazingfishthathavebeenaroundsincelongbeforethedinosaursexisted.Theyliveinwatersallovertheworld,ineveryocean,andeveninsomeriversandlakes.SharksandbonyfishUnlikebonyfish,sharkshavenobones;theirskeletonismadeofcartilage(软骨),whichisatough,fibroussubstance,notnearlyashardasbone.Cartilage,astrongfibrous(纤维的)substance,issofterthanbone;ournoseandearsaremadeofcartilage.Sharksalsohavenoswimbladder(unlikebonyfish).SizeTherearemanydifferentspeciesofsharksthatrangeinsizefromthesizeofaperson'shandtobiggerthanabus.TheWhalesharkisthelargestfishintheworld;thebaskingsharkisthesecondlargestfish.Fully-grownsharksrangeinsizefrom7incheslong(theSpinedPygmyshark),upto50feetlong.Mostsharksareintermediateinsize,andareaboutthesamesizeaspeople,5-7feetlong.Halfofthesharkspeciesareunder39incheslong.VarietyofsharksThereareabout368differentspeciesofsharks,whicharedividedinto30families.Thesedifferentfamiliesofsharksareverydifferentinthewaylook,live,andeat.Theyhavedifferentshapes,sizes,color,fins,teeth,habitat,diet,personality,methodofreproduction,andotherattributes.Sometypesofsharkarevery.rareandsomearequitecommon.Thespinydogfishsharkisthemostcommonshark.BodyshapesSharkshaveavarietyofbodyshapes.Mostsharkshavestreamlined(流线型的),Somesharkshaveanelongatedbodyshape(e.g.,cookiecuttersharksandwobbegongs).Sawsharkshaveelongatedsnouts,threshersharkshaveatremendouslyelongateduppertailfinwhichtheyusetostunprey,andhammerheadshaveextraordinarilywideheads.Thegoblinsharkhasalarge,pointedprotuberance(突出)onitshead;itspurposeisunknown.TakeapassagefromCET4forexample.TeethTheteethofsharksarealsostriking.Sharksmayhaveupto3,000teethatonetime.Mostsharksdonotchewtheirfood,butswallowitdownwholeorinlargepieces.Theteetharearrangedinrows;whenonetoothisdamagedorlost,itisreplacedbyanother.Mostsharkshaveabout5rowsofteethatanytime.Thefrontsetisthelargestanddoesmostofthewok.DietSharksvarygreatlyintheirdiets,buttheyareallcarnivores(食肉动物).Someeatfish,othersharks,andmarinemammals;someeatshellfishfromtheoceanfloor;andotherseattinybitsofplankton(浮游动物)andsmallanimalsfromthewaterastheyswimwithopenmouths.Theyeathugeamountsofthesetinyanimalsandplants.Sharks'attacksWhensomesharks(liketheGreatWhiteortheGrayReefshark)turnaggressivepriortoanattack,theyarchtheirbackandthrowbacktheirhead.Theyalsomovetheirtailmoreacutely(probablyinpreparationforachase).Sharksdonotnormallyattackpeople,andonlyabout25speciesofsharksareknowntoattackpeople.Sharksattackfewerthan100peopleeachyear.Manymorepeoplearekilledbybeesorlightning.Thesharksthatarethemostdangeroustopeoplearethegreatwhiteshark,thetigershark,thebullshark,andtheoceanicwhitetipshark.Thebullsharkisthemostfrequentattackerofpeopleasitswimsinveryshallowwaterswherepeopleswimandisaveryplentifulshark.Someoftheothersharksthatareknowntohaveattackedpeopleincludethegrayshark,blueshark,hammerheadshark,makoshark,nurseshark,lemonshark,blacktipreefshark,wobbegongs,sandtiger,spittingsharks,andtheporbeagle.Somepeoplebelievethatsharksmistakepeople(especiallypeopleswimmingonsurfboards)forsealsandsealions,someoftheirfavoritefoods.Occasionally,agroupofsharkswillattackafoodsource(forexample,aschooloffish)inamaniacalfashion.Theywillwildlyattackthefoodandanythinginthearea,eveneachother,sometimeswoundingoreatingfellowsharks.HabitatSharksliveinoceansandseasallovertheworld,andeveninsomeriversandlakes,especiallyinwarmerwaters.Somesharkslivenearthesurface,somelivedeepinthewater,andothersliveonorneartheoceanfloor.Pelagic(远洋的)sharks(livingintheopenocean)includethegreatwhiteshark,thebaskingshark,etc.Benthicsharks(livingattheoceanfloor)includethezebrahornshark,thewohhegongs,andtheangelshark,whichusuallyhaveflattened,camouflaged(伪装的)bodiesthatletthemhideintheseabed.SomesharksevenventuremanymilesupintothefreshwaterofriversliketheMississippiintheUSAandtheArhazoninBrazil.Thebullshark(Carcharhinusleucas)sometimesventuresintofreshwater.MigrationofsharksSomesharksliveinrelativelywarmwaters(hammerheads,bullsharks,andtigersharks).Othersharks,suchasthethresher,mako,baskingandblueshark,liveintemperatewater(whichisneitherhotnorcold).Others,includingthedogfish,Greenland,andgoblin,liveincoolwaters.SomesharksstayinthesameregionintheirentirelivesWhileotherstravelacrossoceans.Therearethreedifferenttypesofsharkswhenitcomestomigratory(迁移的)patterns:localsharks,coastalpelagicsharks,andhighlypelagicsharks.Localsharksdonotmigrate,andrangeonlyaboutahundredmilesfromtheirhabitat,coastalpelagicsharkscanmigrateover1,000miles,whilehighlypelagicsharksmigrateacrossoceans.EvolutionofsharksSharkshaveexistedforover350millionyears.Theyevolvedover100millionyearsbeforethedinosaursdid.Thiswaslongbeforepeopleevolved.Mostfossilevidenceofearlysharksisfromfossilizedteethandafewskinimpressions.Cladodonts,primitivesharks,haddouble-pointedteeth,wereupto6feetlonglivedabout360millionyearsago;theyatefishandcrustaceans(甲壳类).Megalodonwasanancient,meat-eatingshar