小编为备考的同学们整理了2019年12月英语四级阅读练习题(10)，希望可以为大家带来帮助，预祝大家高分通过。

Whenbloodissenttothelungsbytheheart,ithascomebackfromthecellsintherestofthebody.Sothebloodthatgoesintothewallofanairsac(Jl)containsmuchdissolvedcarbondioxidebutverylittleoxygen.Atthesametime,theairthatgoesintotheairsaccontainsmuchoxygenbutverylittlecarbondioxide.Youhavelearnedthatdissolvedmaterialsalwaysdiffuse(扩散)fromwherethereismoreofthemtowherethereisless.Oxygenfromtheairdissolvesinthemoistureontheliningoftheairsacanddiffusesthroughtheliningintotheblood.Meanwhile,carbondioxidediffusesfromthebloodintotheairsac.Thebloodthenflowsfromthelungsbacktotheheart,whichsendsitouttoallotherpartsofthebody.

Soonafterairgoesintoanairsac,itgivesupsomeofitsoxygenandtakesinsomecarbondioxidefromtheblood.Tokeepdiffusiongoingasitshould,thiscarbondioxidemustbegottenridof.Breathing,whichiscausedbymovementsofthechest,forcestheusedairoutoftheairsacsinyourlungsandbringsinfreshair.Thebreathingmusclesarecontrolledautomaticallysothatyoubreatheattheproperratetokeepyourairsacssuppliedwithfreshair.Ordinarily,youbreatheabouttwenty-twotimesaminute.Ofcourse,youbreathefasterwhenyouareexercisingandslowerwhenyouareresting.Freshairisbroughtintoyourlungswhenyoubreathein,orinhale,whileusedairisforcedoutofyourlungswhenyoubreatheout,orexhale.

26.Intherespiratoryprocess,onlyoneofthefollowingactionstakesplace:itis_______.

A.thediffusionofbloodthroughcapillarywallsintoairsacsB.thediffusionofcarbondioxidethroughcapillaryandairsacwallsintothebloodC.thediffusionofoxygenthroughtheairsacandcapillarywallsintothebloodD.theexchangeofnitrogenwithinairsacs

27.Thenumberoftimesperminutethatyoubreatheis_______.A.independentofyourrateofexerciseB.fixedattwenty-twotimesperminuteC.influencedbyyourageandsexD.controlledautomaticallybyanunspecifiedbodymechanism

28.TheprocessbywhichcarbondioxideandoxygenaretransferreddoesnotdependonA.thepresenceofnitrogeninthebloodB.breathingmusclesC.theflowofbloodD.themoistureintheairsaclinings

29.Theauthor'sstyleinthispassagecanbestbedescribedas---------.AinformalandmatteroffactB.impersonalC.personalP-matteroffactandformal30.Whichofthefollowingwordscanreplacetheword"exhale"?A.Breatheout.B.Breathein.C.Diffuse.D.Exchange.

26.C27.D28.A29.A30.A