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1、江西南昌市2016高考英语（二轮）阅读理解选练（4〉及答案闻篠理鮮---科普常识类Belowisaselectionfromapopularsciencehook.Ifbloodisred,whyareveins（静脉）blue?Actually,veinsarenotblueatall.Theyaremoreofaclear,yellowishcolour.Althoughbloodlooksredwhenitsoutsidethebody,whenitssittinginaveinnearthesurfaceoftheskin,it'smoreofadarkredd
2、ishpurplecolou匚Attherightdepth,theseblood-filledveinsreflectlessredlightthanthesurroundingskin,makingthemlookbluebycomparison.Whichworksharder,yourheartoryourbrain?ThatkindofdependsonwhetheryouTebusythinkingorbusyexercising.Yourheartworksuptothreetimesharderduringexercise,andshiftsenough
3、bloodoveralifetimetofillasupertanke匚But,inthelongrun,yourbrainprobablytipsit,becauseevenwhenyouTesittingstillyourbrainisusingtwiceasmuchenergyasyourheart,andittakesfourtofivetimesasmuchbloodtofeedit.Whydoteethfallout,andwhydon'ttheygrowbackingrown-ups?Baby（or“milk"）teethdonotlastlong；the
4、yfallouttomakeroomforbigger,strongeradultteethlateron.Adultteethfalloutwhentheybecomedamaged,decayedandinfectedbybacteria.Oncethissecondsetofteethhasgrownin,yoifredone.Whenthey'regone,they'regone.Thisisbecausenaturefiguresyou'resetforlife,andwhatcontrolsregrowthofyourteethswitchesoff.Doo
5、ldpeopleshrinkastheyage?Yesandno.Manypeopledogetshorterastheyage.But,whentheydo,itisn'tbecausethey'reshrinkingallove匚Theysimplyloseheightastheirspine（脊*主）becomesshorterandmorecurvedduetodisuseandtheeffectsofgravity（重力）.Many（butnotall）menandwomendoloseheightastheygetolder.Menloseanaverage
6、of3-4cminheightastheyage,whilewomenmaylose5cmormore.Ifyoulivetobe200yearsold,wouldyoukeepshrinkingtillyouwere,like60cmtail,likealittleboyagain?No,becauseoldpeopledon'treallyshrink!Itisnotthattheyaregrowingbackwards一theirlegs,armsandbackbonesgettingshorter.Whentheydogetshorter,itsbecauset
7、hespinehasshortenedalittle.Or,moreoften,becomemorebentandcurved.Whydoesspinningmakeyoudizzy（眩晕的）？BecauseyourbraingetsconfusedbetweenwhatyouYeseeingandwhatyourrefeeling.Thebrainsensesthatyourrespinningusingspecialgravity-and-motion-sensingorgansinyourinnerear,whichworktoge
