网络计划不能明确地反映出各项工作之间错综复杂的逻辑关系，不便于对各工作提前或拖延的影响进行分析及动态控制。

双代号网络图以节点及其编号表示工作，以箭线表示工作之间的逻辑关系。

8.关于GNSS测量的技术设计，下面说法正确的是

18.采用空气间层进行隔声时,中间空气层的厚度以()为宜。

由于科技进步而不端出现性能更完善、生产效率更高的设备，使原有的设备显得陈旧落后，因此产生经济默算称为()磨损

企业采用严格的信用标准，虽然会增加应收账款的机会成本，但能扩大商品销售额，从而给企业带来更多的收益。（）

IRR是指能使投资方案的NPV=0时的贴现率

18层的房屋优先采用下列哪种结构体系（）

18层的房屋优先采用框架剪力墙体系。（）

AnaccidentthatoccurredintheskiesovertheGrandCanyonin1956resultedintheestablishmentoftheFederalAviationAdministration(FAA)toregulateandoverseetheoperationofaircraftintheskiesovertheUnitedStates,whichwerebecomingquitecongested.TheresultingstructureofairtrafficcontrolhasgreatlyincreasedthesafetyofflightintheUnitedStates,andsimilarairtrafficcontrolproceduresarealsoinplaceovermuchoftherestoftheworld.Rudimentaryairtrafficcontrol(ATC)existedwellbeforetheGrandCanyondisaster.Asearlyasthe1920s,theearliestairtrafficcontrollersmanuallyguidedaircraftinthevicinityoftheairports,usinglightsandflags,whilebeaconsandflashinglightswereplacedalongcross-countryroutestoestablishtheearliestairways.However,thispurelyvisualsystemwasuselessinbadweather,and,bythe1930s,radiocommunicationwascomingintouseforATC.Thefirstregiontohavesomethingapproximatingtoday'sATCwasNewYorkCity,withothermajormetropolitanareasfollowingsoonafter.Inthe1940s,ATCcentrescouldanddidtakeadvantageofthenewlydevelopedradarandimprovedradiocommunicationbroughtaboutbytheSecondWorldWar,butthesystemremainedrudimentary.ItwasonlyafterthecreationoftheFAAthatfull-scaleregulationofAmerica'sairspacetookplace,andthiswasfortuitous,fortheadventofthejetenginesuddenlyresultedinalargenumberofveryfastplanes,reducingpilots'marginoferrorandpracticallydemandingsomesetofrulestokeepeveryonewellseparatedandoperatingsafelyintheair.ManypeoplethinkthatATCconsistsofarowofcontrollerssittinginfrontoftheirradarscreensatthenation'sairports,tellingarrivinganddepartingtrafficwhattodo.Thisisaveryincompletepartofthepicture.TheFAArealisedthattheairspaceovertheUnitedStateswouldatanytimehavemanydifferentkindsofplanes,flyingformanydifferentpurposes,inavarietyofweatherconditions,andthesamekindofstructurewasneededtoaccommodateallofthem.Tomeetthischallenge,thefollowingelementswereputintoeffect.First,ATCextendsovervirtuallytheentireUnitedStates.Ingeneral,from365mabovethegroundandhigher,theentirecountryisblanketedbycontrolledairspace.Incertainareas,mainlynearairports,controlledairspaceextendsdownto215mabovetheground,and,intheimmediatevicinityofanairport,allthewaydowntothesurface.ControlledairspaceisthatairspaceinwhichFAAregulationsapply.Elsewhere,inuncontrolledairspace,pilotsareboundbyfewerregulations.Inthisway,therecreationalpilotwhosimplywishestogoflyingforawhilewithoutalltherestrictionsimposedbytheFAAhasonlytostayinuncontrolledairspace,below365m,whilethepilotwhodoeswanttheprotectionaffordedbyATCcaneasilyenterthecontrolledairspace.TheFAAthenrecognisedtwotypesofoperatingenvironments.Ingoodmeteorologicalconditions,flyingwouldbepermittedunderVisualFlightRules(VFR,视觉飞行规则),whichsuggestsastrongrelianceonvisualcuestomaintainanacceptablelevelofsafety.PoorvisibilitynecessitatedasetofInstrumentalFlightRules(IFR,仪表飞行规则),underwhichthepilotreliedonaltitudeandnavigationalinformationprovidedbytheplane'sinstrumentpaneltoflysafely.Onaclearday,apilotincontrolledairspacecanchooseaVFRorIFRflightplan,andtheFAAregulationsweredevisedinawaywhichaccommodatesbothVFRandIFRoperationsinthesameairspace.However,apilotcanonlychoosetoflyIFRiftheypossessaninstrumentratingwhichisaboveandbeyondthebasicpilot'slicensethatmustalsobeheld.onaltitudeandnavigationalinformationprovidedbytheplane'sinstrumentpaneltoflysafely.Onaclearday,apilotincontrolledairspacecanchooseaVFRorIFRflightplan,andtheFAAregulationsweredevisedinawaywhichaccommodatesbothVFRandIFRoperationsinthesameairspace.However,apilotcanonlychoosetoflyIFRiftheypossessaninstrumentratingwhichisaboveandbeyondthebasicpilot'slicensethatmustalsobeheld.Controlledairspaceisdividedintoseveraldifferenttypes,designatedbylettersofthealphabet.UncontrolledairspaceisdesignatedClassF,whilecontrolledairspacebelow5,490mabovesealevelandnotinthevicinityofanairportisClassE.Allairspaceabove5,490misdesignatedClassA.ThereasonforthedivisionofClassEandClassAairspacestemsfromthetypeofplanesoperatinginthem.Generally,ClassEairspaceiswhereonefindsgeneralaviationaircraft(fewofwhichcanclimbabove5,490manyway),andcommercialturbopropaircraft.Above5,490mistherealmoftheheavyjets,sincejetenginesoperatemoreefficientlyathigheraltitudes.ThedifferencebetweenClassEandAairspaceisthatinClassA,alloperationsareIFR,andpilotsmustbeinstrument-rated,thatis,skilledandlicensedinaircraftinstrumentation.ThisisbecauseATCcontroloftheentirespaceisessential.Threeothertypesofairspace,ClassesD,CandB,governthevicinityofairports.Thesecorrespondroughlytosmallmunicipal,medium-sizedmetropolitanandmajormetropolitanairportsrespectively,andencompassanincreasinglyrigoroussetofregulations.Forexample,allaVFRpilothastodotoenterClassCairspaceisestablishtwo-wayradiocontactwithATC.NoexplicitpermissionfromATCtoenterisneeded,althoughthepilotmustcontinuetoobeyallregulationsgoverningVFRflight.ToenterClassBairspace,suchasonapproachtoamajormetropolitanairport,anexplicitATCclearance(飞机起降的许可)isrequired.Theprivatepilotwhocruiseswithoutpermissionintothisairspaceriskslosingtheirlicense.18.BeaconsandflashinglightsarestillusedbyATCtoday.

假定玉米市场的需求是缺乏弹性的，玉米的产量等于销售量且等于需求量，恶劣的气候条件使玉米产量下降20%，在这种情况下

项目融资与风险投资的相同之处有（）。

18、固定成本具有的特征是（）。

当今世界各国行使的税收管辖权通常有（）。

18.有程序如下：#include<stdio.h>structcmplx{intx;inty;}cnum[2]={1,3,2,7};intmain(){printf("%d\n",cnum[0].y/cnum[0].x*cnum[1].x);return0;}该程序执行后输出的结果是