GMAT考试阅读理解.docx

GMAT考试阅读理解

如果惧怕前面跌宕的山岩，生命就永远只能是死水一潭。以下是小编为大家搜索整理的2017年GMAT考试阅读理解，希望能给大家带来帮助，更多精彩内容请及时关注我们应届毕业生考试网! Interrestrialenvironments,gravityplacesspecialdemandsonthecardiovascularsystemsofanimals.Gravitationalpressurecancausebloodtopoolinthelowerregionsofthebody,makingitdifficulttocirculatebloodtocriticalorganssuchasthebrain.Terrestrialsnakes,inparticular,exhibitadaptationsthataidincirculatingbloodagainsttheforceofgravity. Theproblemconfrontingterrestrialsnakesisbestillustratedbywhathappenstoseasnakeswhenremovedfromtheirsupportivemedium.Becausetheverticalpressuregradientswithinthebloodvesselsarecounteractedbysimilarpressuregradientsinthesurroundingwater,thedistributionofbloodthroughoutthebodyofseasnakesremainsaboutthesameregardlessoftheirorientationinspace,providedtheyremainintheocean.Whenremovedfromthewaterandtiltedatvariousangleswiththeheadup,however,bloodpressureattheirmidpointdropssignificantly,andatbrainlevelfallstozero.Thatmanyterrestrialsnakesinsimilarspatialorientationsdonotexperiencethiskindofcirculatoryfailuresuggeststhatcertainadaptationsenablethemtoregulatebloodpressuremoreeffectivelyinthoseorientations. Onesuchadaptationisthecloserproximityoftheterrestrialsnake'shearttoitshead,whichhelpstoensurecirculationtothebrain,regardlessofthesnake'sorientationinspace.Theheartofseasnakescanbelocatednearthemiddleofthebody,apositionthatminimizestheworkentailedincirculatingbloodtobothextremities.Inarborealsnakes,however,whichdwellintreesandoftenassumeaverticalposture,theaveragedistancefromthehearttotheheadcanbeaslittleas15percentofoverallbodylength.Suchalocationrequiresthatbloodcirculatedtothetailofthesnaketravelagreaterdistancebacktotheheart,aproblemsolvedbyanotheradaptation.Whenclimbing,arborealsnakesoftenpausemomentarilytowiggletheirbodies,causingwavesofmmusclecontractionthatadvancefromthelowertorsotohead.Bycompressingtheveinsandforcingbloodforward,thesecontractionsapparentlyimprovetheflowofvenousbloodreturningtotheheart. 文章概况:文章第一段开头说地球的重力对血液循环造成一定的影响,而结尾举了一个蛇的例