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1、108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).Veryoccasionallytherockss
2、howimpressionofskin,sothat,apartfromcolor,wecanbuildupareasonablyaccuratepictureofananimalthatdiedmillionsofyearsago.Thatkindofrockinwhichtheremainsarefoundtellsusmuchaboutthenatureoftheoriginalland,oftenoftheplantsthatgrewonit,andevenofitsclimate.2).Ne
3、arlyallofthefossilsthatweknowwerepreservedinrocksformedbywateraction,andmostoftheseareofanimalsthatlivedinornearwater.Thusitfollowsthattheremustbemanykindsofmammals,birds,andinsectsofwhichweknownothing.3).Therewerealsocrablikecreatures,whosebodieswereco
4、veredwithahornysubstance.Thebodysegmentseachhadtwopairsoflegs,onepairforwalkingonthesandybottom,theotherforswimming.Theheadwasakindofshieldwithapairofcompoundeyes,oftenwiththousandsoflenses.Theywereusuallyaninchortwolongbutsomewere2feet.4).Ofthese,theam
5、monitesareveryinterestingandimportant.Theyhaveashellcomposedofmanychambers,eachrepresentingatemporaryhomeoftheanimal.Astheyounggrewlargeritgrewanewchamberandsealedoffthepreviousone.ThousandsofthesecanbeseenintherocksontheDorsetCoast.5).About75millionyea
6、rsagotheAgeofReptileswasoverandmostofthegroupsdiedout.Themammalsquicklydeveloped,andwecantracetheevolutionofmanyfamiliaranimalssuchastheelephantandhorse.Manyofthelatermammalsthoughnowextinct,wereknowntoprimitivemanandwerefeaturedbyhimincavepaintingsando
7、nbonecarvings.[A]Theshellfishhavealonghistoryintherockandmanydifferentkindsareknown.1001[B]Nevertheless,weknowagreatdealaboutmanyofthembecausetheirbonesandshellshavebeenpreservedintherocksasfossils.Fromthemwecantelltheirsizeandshape,howtheywalked,thekin
8、doffoodtheyate.[C]Thefirstanimalswithtruebackboneswerethefishes,firstknownintherocksof375millionyearsago.About300millionyearsagotheamphibians,theanimalsabletolivebothonlandandinwater,appeared.Theyweregiant,sometimes8feetlong,andm
