PassageThree
Questions31to35arebasedonthefollowingpassage.
Inthelate1960'smanypeopleinNorthAmericaturnedtheirattentiontoenvironmentalproblems，andnewsteel-and-glassskyscrapers(摩天楼)werewidelycriticized.Scientistspointedoutthatblocksoftallbuildingsinacityoftenoverburdens.publictr ansportationandparkinglotcapacities.
Skyscrapersarealsobigconsumers，andwasters，ofelectr icpower.Inonerecentyear.theadditionof17millionsquarefeetofskyscraperofficespaceinNewYorkCityraisedthepeakdailydemandforelectr icityby120，000kilowatts-enoughtosupplytheentirecityofAlbany，NewYork，foraday.
Glass-walledskyscraperscanbeespeciallywasteful.Theheatloss(orgain)throughawallofhalf-inchplateglassismorethantentimesthatthroughatypicalbrickwallfilledwithinsulationboard.Tolessenthestr ainonheatingandair-conditioningequipment，buildersofskyscrapershavebeguntousedouble-glazed(装上玻璃的)panelsofglass，andreflectiveglassescoatedwithsilverorgoldmirrorfilmsthatr educeglareaswellasheatgain.However.mirror-walledskyscrapersraisethetemperatureofthesurroundingairandaffectneighboringbuildings.
Skyscrapersputaseverestr ainonacity'ssanitation(卫生)facilities，too.Iffullyoccupied,thetwoWorldTradeCentertowersinNewYorkCitywouldalonegenerate2.25milliongallonsofrawwasteseachyear-asmuchasacitythesizeofStamford，Connecticut，whichhasapopulationofmorethan109，000.
Skyscrapersalsointerferewithtelevisionreception，blockbirdflyways，andobstr uctairtr affic.InBostoninthelate1960's，somepeopleevenfearedthatshadowsfromskyscraperswouldkillthegrassonBostonCommon.
Still，peoplecontinuetobuildskyscrapersforallthereasonsthattheyhavealwaysbuiltthem-personalambition(抱负)pride，andthedesireofownerstohavethelargestpossibleamountofrentable space.
Themainpurposeofthepassageisto______.
A.compareskyscraperswithothermodemstr uctures
B.describeskyscrapersandtheireffectontheenvironment
C.advocatetheuseofmasonry(化妆舞会)intheconstr uctionofskyscrapers
D.illustr atesomearchitecturaldesignsofskyscrapers
正确答案：B[解析]见本文第一句话，开篇点题“摩天楼及它们对周围环境的影响”。
