2016年6月英语四级考试：仔细阅读练习(3)思维导图
Agriculture is the number one industry in the United States and agricultural products are the country's leading export. American farmers manage to feed not only the total populati
树图思维导图提供 2016年6月英语四级考试：仔细阅读练习(3) 在线思维导图免费制作，点击“编辑”按钮，可对 2016年6月英语四级考试：仔细阅读练习(3) 进行在线思维导图编辑，本思维导图属于思维导图模板主题，文件编号是：8abeeb97aa251fc0d8e9cf86fe04b4d5
思维导图大纲
2016年6月英语四级考试：仔细阅读练习(3)思维导图模板大纲
AgricultureisthenumberoneindustryintheUnitedStatesandagriculturalproductsarethecountry'sleadingexport.AmericanfarmersmanagetofeednotonlythetotalpopulationoftheUnitedStates,butalsomillionsofotherpeoplethroughouttherestoftheworld.Cornandsoybeanexportsaloneaccountforapproximately75percentoftheamountsoldinworldmarkets.
Thisproductivity,however,hasitsprice.Intensivecultivationexposestheearthtothedamagingforcesofnature.Everyyearwindandwaterremovetonsofrichsoilfromthenation'scroplands.
Eachfieldiscoveredbyalimitedamountoftopsoil,theupperlayerofearthwhichisrichestinthenutrientsandmineralsnecessaryforgrowingcrops.EversincethefirstfarmersarrivedintheMidwestalmost200yearsago，cultivationand,consequently,erosionhavebeendecreasingthesupplyoftopsoil.Inthe1830s,nearlytwofeetofrich,blacktopsoilcoveredtheMidwest.Todaytheaveragedepthisonlyeightinches,andeverydecadeanotherinchisblownorwashedaway.Thiserosionissteadilydecreasingtheproductivityofvaluablecropland.AUnitedStatesAgriculturalDepartmentsurveystatesthatiferosioncontinuesatitspresentrate,cornandsoybeanyieldsintheMidwestmaydropasmuchas30percentoverthenext50years.
Sofar,farmershavebeenabletocompensateforthelossoffertiletopsoilbyapplyingmorechemicalfertilizerstotheirfields;however,whilethispracticehasincreasedcropyields,ithasbeendevastatingforecology.Agriculturehasbecomeoneofthebiggestpollutersofthenation'spreciouswatersupply.Rivers,lakes,andundergroundreservesofwaterarebeingfilledinandpoisonedbysoilandchemicalscarriedbydrainagefromerodingfields.Furthermore,fertilizersonlyreplenishthesoilstheydonotpreventitsloss.
26.Thelastsentenceinthefirstparagraphgivesanexampletoshow_______.
A.thatAmericanfarmersmanagetofeedthetotalpopulationoftheU.S.
B.theleadingpositionoftheU.S.farmingintheworld
C.howimportantAmericanpeopleconsidertheirfarming
D.thatmanypeopleintheworldrelyontheexportoftheagriculturalproductsoftheU.S.A.
27.Inordertocompensateforthelossoffertiletopsoil,farmershavebeen_______.
A.plantinglesscornandsoybeanB.puttingfertilizersontheirfields
C.preventingsoilerosionD.decreasingthesupplyoftopsoil
28.Atthepresentrate,approximatelyhowmanyyearslatertheblacktopsoilnowcoveringtheMidwestwillcompletelybeblownorwashedaway?
A.120yearslater..B.80yearslater.
C.50yearslater.D.100yearslater.
29."Thispractice"inParagraph4refersto_______.
A.thatfarmershaveloweredtheyieldofcornandsoybean
B.thatfarmershaveexpandedcroplands
C.thatfarmershaveappliedmorechemicalfertilizers
D.thatthetopsoilhasbeendecreasedgreatly
30.AllofthefollowingarestatementsaboutthedisadvantagesoffertilizersEXCEPTthat________.
A.theyreplenishthesoilB.theydonotpreventthelossofsoil
C.theyaredestroyingtheecologyD.theypollutethenation'swatersupply
答案：26.D27.B28.B29.C30.A
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