一般火灾探测器的工作温度为（）。 A: 0～50℃ B: -10～50℃ C: -40～50℃ D: -50～50℃

在VB语言中，表示"50>y>-50"的正确表达式是（）。 A: 50>y>-50 B: 50>y and y>-50 C: 50>y or y>-50 D: 50>y or y<-50

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.

双氧水浓度范围是（）。 A: 30%-50% B: 35%-50% C: 40%-50% D: 45%-50%定

下面()选项中的两个数相等。 A: =50%和=5/100 B: =50%和=50/100 C: =“50%”和=“50/100” D: =“50%”和=50/100

下面选项中（）两个值是相等的。 A: =50%和=5/l00 B: =50%和=50/l00 C: ="50%"和="50/l00" D: ="50%"和=50/l00

The earth is nearly ______ the moon. A: 50 time the size of B: 50 times the size of C: 50 times as size as D: 50 times as that of

MOSFET适用于( )。 A: 8~50kHz B: 50~200kHz C: 50~400kHz D: 50~5MHz

新生儿中度硬肿的范围是 A: 10%～50% B: 20%～50% C: 30%～50% D: 40%～50% E: 50%以上

杂交方式A/B//C中，A和C的遗传比重分别是多少（ ）。 A: 50%，25% B: 50%，50% C: 25%，50% D: 25%，25%