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阅读理解Whennatureisleftaloneabalanceisreachedamongtheanimalsandplantslivinginonearea.Butwhenmanstartshisworkinnaturethebalanceislikelytobedestroyed.Hegrowsa
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(1)

阅读理解

Whennatureisleftaloneabalanceisreachedamongtheanimalsandplantslivinginonearea.Butwhenmanstartshisworkinnaturethebalanceislikelytobedestroyed.Hegrowsacropandtakesitawaytoeat;thentherearenodeadleavestofallonthegroundholdingwaterwhileitsinksintothesurfaceordecaying(腐烂)andaddinghumus(腐殖质)tothesoil.Unlessafarmeractswithknowledgeandskillheisthereforemostlikelytomakethelandpoorer.Totaketheplaceoftheusefulmatterinthecropsthatheremovesheusessomekindoffertilizer.Chemicalfertilizersareofgreathelpbutthewasteproductsofanimalsanddecayingremainsofplantsshouldalsobeputontheland.Insomeplacesitisahabittoburnwastemateriallyingaboutbutsuchburningdestroystheusefulmatterinthedeadplants.Althoughtheashesthatareleftarevaluablewhenputonthelandabetterpracticeistoburythewastesothatitdecaysandincreasesthehumusinthesoil.

Inthepastwhentheworldpopulationwasmuchlowerthanitisnowamanhadlittledifficultyinordinarytimesingrowingthefoodthatwasneeded.Whenafieldhadbeenusedsomeyearsandhadbecometiredthefarmercouldmovetoanotherplace.Thetiredlandthenslowlyrecovered.Graduallygrassesandotherplantswouldappearonitanditsproductivepowerwouldslowlyreturntonormalthroughtheirdecay.Butnatureleftalonewouldtakealongtimetobringbackthelandtoitsformerstate;thelengthoftimerequiredwoulddependonlocalconditionsbutitmightwellbetenyears.

Itisabadpracticetogrowthesamecropinafieldyearafteryear.Ifthecropischangedthelandwillsufferlessbecauseitistreatedandusedinadifferentway.Differentplantshavedifferenteffectsonthesoil.Thereforeachangeofcropwilldolessharmthanthegrowingofthesamecropyearafteryearandaregularchangetograsswilldogoodtothesoil.Muchwillthereforebegainedifdifferentcropsaregrownoneafteranotheramethodknownastherotation(轮作)ofcrops.

盛立回答:
  答案:1.A;2.C;3.B;4.D;
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