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1、08考研英语知识点每周答疑一、答疑之“七选五”分析：LongbeforeManlivedontheEarth,therewerefishes,reptiles,birds,insects,andsomemammals.Althoughsomeoftheseanimalswereancestorsofkindslivingtoday,othersarenowextinct,thatis,theyhavenodescendantsalivenow.1).Veryoccasionallytherocksshowimpressionofs
2、kin,sothat,apartfromcolor,wecanbuildupareasonablyaccuratepictureofananimalthatdiedmillionsofyearsago.Thatkindofrockinwhichtheremainsarefoundtellsusmuchaboutthenatureoftheoriginalland,oftenoftheplantsthatgrewonit,andevenofitsclimate.2).Nearlyallofthefossilsthatweknowwe
3、represervedinrocksformedbywateraction,andmostoftheseareofanimalsthatlivedinornearwater.Thusitfollowsthattheremustbemanykindsofmammals,birds,andinsectsofwhichweknownothing.3).Therewerealsocrablikecreatures,whosebodieswerecoveredwithahornysubstance.Thebodysegmentseachha
4、dtwopairsoflegs,onepairforwalkingonthesandybottom,theotherforswimming.Theheadwasakindofshieldwithapairofcompoundeyes,oftenwiththousandsoflenses.Theywereusuallyaninchortwolongbutsomewere2feet.4).Ofthese,theammonitesareveryinterestingandimportant.Theyhaveashellcomposedo
5、fmanychambers,eachrepresentingatemporaryhomeoftheanimal.Astheyounggrewlargeritgrewanewchamberandsealedoffthepreviousone.ThousandsofthesecanbeseenintherocksontheDorsetCoast.5).About75millionyearsagotheAgeofReptileswasoverandmostofthegroupsdiedout.Themammalsquicklydevel
6、oped,andwecantracetheevolutionofmanyfamiliaranimalssuchastheelephantandhorse.Manyofthelatermammalsthoughnowextinct,wereknowntoprimitivemanandwerefeaturedbyhimincavepaintingsandonbonecarvings.[A]Theshellfishhavealonghistoryintherockandmanydifferentkindsareknown.[B]Neve
7、rtheless,weknowagreatdealaboutmanyofthembecausetheirbonesandshellshavebeenpreservedintherocksasfossils.Fromthemwecantelltheirsizeandshape,howtheywalked,thekindoffoodtheyate.[C]Thefirstanimalswithtruebackboneswerethefishes,firstknownintherocksof375millionyearsago.About
8、300millionyearsagotheamphibians,theanimalsabletolivebothonlandandinwater,appeared.Theyweregiant,sometimes8feetlong,andmanyof
