We all know that it is possible for

根据考试中心的统计分析，以下试题在2019/9/4日高考习题练习中，答错率较高，为：77%
【单选题】Weallknowthatitispossibleforordinarypeopletomaketheirhomesontheequator(赤道),althoughoftentheymayfeeluncomfortablyhotthere.Millionsdoit.ButasfortheNorthPole(北极)--weknowthatitisnotonlyadangerouslycoldplace,butthatpeoplelikeyouandmewouldfinditquiteimpossibletolivethere.Atthepresenttimeonlythescientistsandexplorerscandoso,andtheyusespecialequipment.Menhadbeentr avelingacrossandaroundtheequatoronwheels,ontheirfeetorinshipsforthousandsofyears;butonlyafewmen,withgreatd ifficultyandinveryrecenttime,haveevercrossedtheicetotheNorthPole.Soitmaysurpriseyoutolearnthat,whentr avelingbyair,itisreallysafertoflyovertheNorthPolethanovertheequator.Ofcourse,thisisnottr ueaboutlandingsinthepolarregion(whichpassengeraeroplanesdonotmake),buttheweather,ifweareflyingataheightof5000metersabovethePole,isadelight.At4000metersandMoreabovetheearthyoucanalwaysbesurethatyouwillnotseeacloudintheskyasfarastheeyecanreach.Inthetr opics(热带),ontheotherhand,youarenotcertaintokeepclearofbadweatherevenatsuchheightsas18000or20000meters.Aeroplanescan’tclimbashighorasquicklyincoldairasinwarmair.Norcanclouds.Inpractice,thisisanadvantagetotheaeroplane,whichisalreadyatagoodheightwhenitr eachesthepolarregionandsodoesnotneedtoclimb,whileatthesametimecoldairkeepsthecloudsdownlow.Aeroplanesusuallydonotneedtoclimbquicklyorflyhighinthepolarregionbecause______.A、theydonotlandthereB、therearenocloudsatallC、theycancrosstheicewithspecialequipmentD、itisverycold
参考答案：B，答错率：77%