TheAmericanbabyboomafterthewarmadeunconvincingU.S.advicetopoorcountriesthattheylimittheirbirths.Howevertherehashardlybeenayearsince1957inwhichbirthratesdidnotfallintheUnitedStatesandotherrichcountri

　　TheAmericanbabyboomafterthewarmadeunconvincingU.S.advicetopoorcountriesthattheylimittheirbirths.Howevertherehashardlybeenayearsince1957inwhichbirthratesdidnotfallintheUnitedStatesandotherrichcountriesandin1976thefallwasespeciallysharp.BothEastGermanyandWestGermanyhavefewerbirthsthantheyhavedeathsandtheUnitedStatesisonlytemporarilyabletoavoidthisconditionbecausethechildrenofthebabyboomarenowanexceptionallylargegroupofmarriedcouples.

　　ItistruethatAmericansdonottypicallyplantheirbirthstosetanexamplefordevelopingnations.Wearemoreaffectedbywomen'sliberation:oncewomenseeinterestingandwell-paidjobsascareersavailabletheyarelesswillingtoprovidefreelaborforchildraising.Fromcostingnothingchildrensuddenlycometoseemimpossiblyexpensive.Andtothehighcostofchildrenareaddedtheuncertaintiesintroducedbydivorce;couplesareincreasingtosubjectchildrentotheterribleexperienceofmarriagebreakdownandthemselvestothedifficultyofraisingachildalone.

　　Thesecircumstances－womenworkingoutsidethehomeandtheinstabilityofmarriagetrendtospreadwithindustrialsocietyandtheywillaffectmoreandmorecountriesduringtheremainderofthiscentury.AlongwiththemgoessocialmobilityambitiontoriseintheurbanworldamainfactorinbringingdownthebirthsinEuropeinthe19thcentury.

　　Foodshortagewillhappenagainwhenthereservesresultingfromthegoodharvestsof1976and1977havebeenconsumed.Urbanizationislikelytocontinuewiththecitiesofthedevelopingnationsstrugglingundertheweightoftwicetheirpresentpopulationsbytheyear2000.Thepresentlyrichcountriesareapproachingastablepopulationlargelybecauseofthechangedplaceofwomenandtheyincidentallyaresettinganexampleofrestrainttotherestoftheworld.Industrialsocietywillspreadtothepoorcountriesandambitionwillexceedresources.Allthiswillleadtoapopulationinthe21stcenturythatissmallerthanthatwasfeared afewyearsago.Forthoseanxioustoseeworldpopulationbroughtundercontrolthenewsisencouraging.

　　49.Duringtheyearsfrom1957to1976thebirthrateoftheUnitedStates_____.

　　A.increased