中国大学MOOC:NobodyreallyknowshowbigLagosis.Whatsindisputableisthatitsgrowingveryquickly.Betweennowand2050,theurbanpopulationofAfricacouldtriple.Yetcitiesinsub-SaharanAfricaarenotgettingricherthewaycitiesintherestoftheworldhave.MosturbanAfricansliveinslums（贫民窟）;migrantsareoftennotmuchbetteroffthantheywereinthecountryside.Why?Theimmediateproblemispoverty.MostofAfricaisurbanisingatalowerlevelofincomethanotherregionsoftheworlddid.Thatmeansthereslittlemoneyaroundforinvestmentthatwouldmakecitiesliveableandmoreproductive.Withoutupgradesandnewcapacity,bridges,roadsandpowersystemsareunabletocopewithexpandingpopulations.WiththeexceptionofSouthAfrica,theonlylightrailmetrosysteminsub-SaharanAfricaisinAddisAbaba,Ethiopia.Trafficjamleadstoexpenseandunpredictability,thingsthatkeepinvestorsaway.Inotherpartsoftheworld,increasingagriculturalproductivityandindustrialisationwenttogether.Moreproductivefarmersmeanttherewasasurplusthatcouldfeedcities;inturn,thatcreatedapooloflabourforfactories.ButAfricancitiesaredifferent.Theyaretoooftenbuiltaroundconsumingnaturalresources.Governmentisconcentratedincapitals,soisthemoney.MosturbanAfricansworkforasmallminorityoftherich,whotendtobeinvolvedineithercronyish（有裙带关系的）businessesorpolitics.SinceAfricanagricultureisstillbroadlyunproductive,foodisimported,consumingaportionofrevenue.Sowhatcanbedone?ThoughAfricancountriesarepoor,notallAfricancitiesare.InLagos,foreignoilworkerscanpayasmuchas65,000dollarsperyearinrentforamodestapartmentinasafepartoftown.Ifthatincomewerebettertaxed,itmightprovidetherevenueforbetterinfrastructure.Ifcityleadersweremoreaccountabletotheirresidents,theymightfavourprojectsdesignedtohelpthemmore.Yetevenasnewroadsarebuilt,newpeoplearrive.Whenacityspopulationgrowsby5%ayear,itisdifficulttokeepup.46.Whatdowelearnfromthepassageaboutcitiesinsub-SaharanAfrica?A.Theyhavemoreslumsthanothercitiesintheworld.B.Theyaregrowingfastwithoutbecomingricher.C.Theyareasmodernisedasmanycitieselsewhere.D.Theyattractmigrantswhowanttobebetteroff.47.Whatdoestheauthorimplyabouturbanisationinotherpartsoftheworld?A.Itbenefitedfromthecontributionofimmigrants.B.Itstartedwhenpeoplesincomewasrelativelyhigh.C.Itbenefitedfromtheacceleratedriseinproductivity.D.Itstartedwiththeimprovementofpeopledlivelihood.48.Whyissub-SaharanAfricaunappealingtoinvestors?A.Itlacksadequatetransportfacilities.B.Thelivingexpensestherearetoohigh.C.Itisonthewholetoodenselypopulated.D.Thelocalgovernmentsarecorrupted.49.InwhatwaydoestheauthorsayAfricancitiesaredifferent?A.Theyhaveattractedhugenumbersoffarmlabourers.B.Theystillrelyheavilyonagriculturalproductivity.C.Theyhavedevelopedattheexpenseofnature.D.Theydependfarmoreonforeigninvestment.50.WhatmightbeasolutiontotheproblemsfacingAfricancities?A.Loweringofapartmentrent.B.Bettereducationforresidents.C.Morerationaloverallplanning.D.Amoreresponsiblegovernment.