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Wecanbeginourdiscussionof“populationasglobalissue”withwhatmostpersonsmeanwhentheydiscuss“thepopulationproblem”:toomanypeopleonearthandatoorapidincreaseinthenumberaddedeachyear.Thefactsarenotindispute,Itwasquiterighttoemploytheanalogythatlikeneddemographicgrowthto“along,thinpowderfusethatburnssteadilyandhaltinglyuntilitfinallyreachesthechargeandexplodes.”
Tounderstandthecurrentsituation,whichischaracterizedbyrapidincreasesinpopulation,itisnecessarytounderstandthehistoryofpopulationtrends.Rapidgrowthisacomparativelyrecentphenomenon.Lookingbackatthe8,000yearsofdemographichistory,wefindthatpopulationshavebeenvirtuallystableorgrowingveryslightlyformostofhumanhistory.Formostofourancestors,lifewashard,oftennasty,andveryshort.Therewashighfertilityinmostplaces,butthiswasusuallybalancedbyhighmortality.Formostofhumanhistory,itwasseldomthecasethatoneintenpersonswouldlivepastforty,whileinfancyandchildhoodwereespeciallyriskyperiods.Often,societieswereincleardangerofextinctionbecausedeathratescouldexceedtheirbirthrates.Thus,thepopulationproblemthroughoutmostofhistorywashowtopreventextinctionofthehumanrace.
Thispatternisimportanttonotice.Notonlydoesitputthecurrentproblemsofdemographicgrowthintoahistoricalperspective,butitsuggeststhatthecauseofrapidincreaseinpopulationinrecentyearsisnotasuddenenthusiasmformorechildren,butanimprovementintheconditionsthattraditionallyhavecausedhighmortality.
Demographichistorycanbedividedintotwomajorperiods:atimeoflong,slowgrowthwhichextendedfromabout8,000BC.tillapproximatelyAD.1650.Inthefirstperiodofsome9600years,thepopulationincreasedfromsome8millionto500millionin1650.Between1650andthepresent,thepopulationhasincreasedfrom500milliontomorethan4billion.Anditisestimatedthatbytheyear2000therewillbe6.2billionpeoplethroughouttheworld.Onewaytoappreciatethisdramaticdifferenceinsuchabstractnumbersistoreducethetimeframetosomethingthatismoremanageable.Between8000BCand1650,anaverageofonly50,000personswasbeingaddedannuallytotheworld’spopulationeachyear.Atpresent,thisnumberisaddedeverysixhours.Theincreaseisabout80,000,000personsannually.
1.Whichofthefollowingdemographicgrowthpatternismostsuitableforthelongthinpowderfuseanalogy?
A.Avirtuallystableorslightlydecreasingperiodandthenasuddenexplosionofpopulation.
B.Aslowgrowthforalongtimeandthenaperiodofrapid,dramaticincrease.
C.Toomanypeopleonearthandafewrapidincreaseinthenumberaddedeachyear.
D.Alongperiodwhendeathratesexceedsbirthratesandthenashortperiodwithhigherfertilityandlowermortality.
2.Duringthefirstperiodofdemographichistory,societieswereoftenindangerofextinctionbecause___.
A.onlyoneintenpersonscouldlivepast40.
B.therewashighermortalitythanfertilityinmostplaces.
C.itwastoodangeroustohavebabiesduetothepoorconditions.
D.ourancestorshadlittleenthusiasmformorechildren.
3.Whichstatementistrueaboutpopulationincrease?
A.Theremightbeanincreaseof2.2billionpersonsfromnowtotheyear2000.
B.About50,000babiesareborneverysixhoursatpresent.
C.Between8000BCandthepresent,thepopulationincreaseisabout80,000,000personseachyear.
D.Thepopulationincreasedfasterbetween8000BCand1650thanbetween1650andthepresent.
4.Theauthorofthepassageintendsto___.
A.warnpeopleagainstthepopulationexplosioninthenearfuture.
B.comparethedemographicgrowthpatterninthepastwiththatafter1650.
C.findoutthecauseforrapidincreaseinpopulationinrecentyears.
D.presentusaclearandcompletepictureofthedemographicgrowth.
5.Theword“demographic”inthefirstparagraphmeans___.
A.statisticsofhuman.
B.surroundingsstudy.
C.accumulationofhuman.
D.developmentofhuman.
Scatteredthroughtheseasoftheworldarebillionsoftonsofsmallplantsandanimalscalledplankton.Mostoftheseplantsandanimalsaretoosmallforthehumaneyetosee.Theydriftaboutlazilywiththecurrents,providingabasicfoodformanylargeranimals.Planktonhasbeendescribedastheequivalentofthegrassesthatgrowonthedrylandcontinents,andthecomparisonisanappropriateone.Inpotentialfoodvaluehowever,planktonfaroutweighsthatofthelandgrasses.Onescientisthasestimatedthatwhilegrassesoftheworldproduceabout49billiontonsofvaluablecarbohydrateseachyear.Thesea’splanktongeneratesmorethantwiceasmuch.
Despiteitsenormousfoodpotential,littleeffortwasmadeuntilrecentlytofarmplanktonaswefarmgrassesonland.Nowmarinescientistshaveatlastbeguntostudythispossibility,especiallyasthesea’sresourcesloomevenmoreimportantasameansoffeedinganexpandingworldpopulation.
Nooneyethasseriouslysuggestedthat“planktonburgers”maysoonbecomepopulararoundtheworld.Asapossiblefarmedsupplementaryfoodsource,however,planktonisgainingconsiderableinterestamongmarinescientists.
Onetypeofplanktonthatseemstohavegreatharvestpossibilitiesisatinyshrimplikecreaturecalledkrill.Growingtotwoorthreeincheslong,krillprovidethemajorfoodforthegiantbluewhale,thelargestanimalevertoinhabittheEarth.Realizingthatthiswhalemaygrow100feetandweigh150tonsatmaturity,itisnotsurprisingthateachonedevoursmorethanonetonofkrilldaily.
Krillswimaboutjustbelowthesurfaceinhugeschoolssometimesmileswide,mainlyinthecoldAntarctic.Becauseoftheirpinkcolor,theyoftenappearasasolidreddishmasswhenviewedfromashiporfromtheair.Krillareveryhighinfoodvalue.Apoundofthesecrustaceanscontainsabout460calories—aboutthesameasshrimporlobster,towhichtheyarerelated.
Ifthekrillcanfeedsuchhugecreaturesaswhales,manyscientistsreason,theymustcertainlybecontendersasnewfoodsourceforhumans.
1.Whichofthefollowingbestportraystheorganizationofthepassage?
A.Theauthorpresentstheadvantagesanddisadvantagesofplanktonasafoodsource.
B.Theauthorquotespublicopiniontosupporttheargumentforfarmingplankton.
C.Theauthorclassifiesthedifferentfoodsourcesaccordingtoamountofcarbohydrate.
D.Theauthormakesageneralstatementaboutplanktonasafoodsourceandthenmovestoaspecificexample.
2.Accordingtothepassage,whyisplanktonregardedtobemorevaluablethanlandgrasses?
A.Itiseasiertocultivate.
B.Itproducesmorecarbohydrates.
C.Itdoesnotrequiresoil.
D.Itismorepalatable.
3.Whydoestheauthormention“planktonburgers”?
A.Todescribetheappearanceofonetypeofplankton.
B.Toillustratehowmuchplanktonawhaleconsumes.
C.Tosuggestplanktonasapossiblefoodsources.
D.Tocomparethefoodvaluesofbeefandplankton.
4.Whatismentionedasoneconspicuousfeatureofkrill?
A.Theyarethesmallestmarineanimals.
B.Theyarepinkincolor.
C.Theyaresimilarinsizetolobsters.
D.Theyhavegrasslikebodies.
5.Theauthormentionsallofthefollowingasreasonswhyplanktoncouldbeconsideredahumanfoodsourceexceptthatitis___.
A.highinfoodvalue.
B.inabundantsupplyintheoceans.
C.anappropriatefoodforotheranimals.
D.freeofchemicalsandpollutants.
