题目内容：
根据以下材料，回答题Inthelate1960s,manypeopleinNorthAmericaturnedtheirattentiontoenvironmentalproblems,andnewsteel-and-glassskyscraperswerewidelycriticized.Ecologistspointedoutthataclusteroftallbuildingsinacityoftentransportationandparkinglotcapacities.
Skyscrapersarealsolavishconsumers,andwastersofelectricpower.Inonerecentyear,theadditionof17millionsquarefeetofskyscraperofficespaceinNewYorkCityraisedthepeakdaily
demandforelectricityby120000kilowatts--enoughtosupplytheentirecityofAlbany,NewYork,foraday.
Glass-walledskyscraperscanbeespeciallywasteful.Theheatloss(orgain)throughawallofhalf-inchplateglassismorethantentimesthatthroughatypicalmasonrywallfilledwithinsula-tionboard.Tolessenthestrainonheatingandair-conditioningequipment,buildersofskyscrapershavebeguntousedouble-glazedpanelsofglass,andreflectiveglassescoatedwithsilverorgoldmirrorfilmsthatreduceglareaswellasheatgain.However,mirror-walledskyscrapersraisethetemperatureofthesurroundingairandaffectneighboringbuildings.
Skyscrapersputaseverestrainonacity'ssanitationfacilities,too.Iffullyoccupied,thetwoWorldTradeCentertowersinNewYorkCitywouldalonegenerate2.25milliongallonsofrawsewage
eachyear-asmuchasacitythesizeofStamford,Connecticut,whichhasapopulationofmorethan109000.
Skyscrapersalsointerferewithtelevisionreception,blockbirdflyways,andobstructairtraf-fic.InBostoninthelate1960s,somepeopleevenfearedthatshadowsfromskyscraperswouldkillthegrassonBostonCommon.
Still,peoplecontinuetobuildskyscrapersforallthe'reasonsthattheyhavealwaysbuiltthem-personalambition,civicpride,andthedesireofownerstohavethelargestpossibleamountofrentablespace.
Themainpurposeofthepassageisto A．discusstheadvantagesanddisadvantagesofskyscrapers
B．compareskyscraperswithothermodernstructures
C．describeskyscrapersandtheireffectontheenvironment
D．illustratevariousarchitectural
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答案解析：