Unit6單元高考閱讀閱讀提示:本文為說明文,講述了二十世紀六十年代BobChristiansen在研究黃石公園的火山歷史時,奇怪地發現到處看不到破火山口的影子,原來,這兒的火山并不是像我們大部分人想象的那種圓錐體形狀的高聳的樣子,而是一個巨大的洞,這個洞太大了以至于從地面水平位置的任何地方都看不見。Inthe1960s,whilestudyingthevolcanichistoryofYellowstoneNationalPark,BobChristiansenbecamepuzzledaboutsomethingthat,oddly,hadnottroubledanyonebefore:hecouldn’tfindthepark’svolcano①.IthadbeenknownforalongtimethatYellowstonewasvolcanicinnature—that’swhataccountedforallitshotspringsandothersteamyfeatures.ButChristiansencouldn’tfindtheYellowstonevolcanoanywhere.Mostofus,whenwetalkaboutvolcanoes,thinkoftheclassiccone(圓維體）shapesofaFujiorKilimanjaro,whicharecreatedwheneruptingmagma(巖衆）pilesup②.Thesecanformremarkablyquickly.In1943,aMexicanfarmerwassurprisedtoseesmokerisingfromasmallpartofhisland.Inoneweekhewastheconfusedownerofaconefivehundredfeethigh.Withintwoyearsithadtoppedoutatalmostfourteenhundredfeetandwasmorethanhalfamileacross.AltogethertherearesometenthousandofthesevolcanoesonEarth,allbutafewhundredofthemextinct.Thereis,however,asecondlessknowntypeofvolcanothatdoesn’tinvolvemountainbuilding.Thesearevolcanoessoexplosivethattheyburstopeninasinglebigcrack,leavingbehindavasthole,thecaldera.Yellowstoneobviouslywasofthissecondtype,butChristiansencouldn’tfindthecalderaanywhere.JustatthistimeNASAdecidedtotestsomenewhigh-altitudecamerasbytakingphotographsofYellowstone.Athoughtfulofficialpassedonsomeofthecopiestotheparkauthoritiesontheassumptionthattheymightmakeaniceblow-upforoneofthevisitors’centers.AssoonasChristiansensawthephotos,herealizedwhyhehadfailedtospotthecaldera:almostthewholepark—2.2millionacres—wascaldera.Theexplosionhadleftaholemorethanfortymilesacross-muchtoohugetobeseenfromanywhereatgroundlevel.AtsometimeinthepastYellowstonemusthaveblownupwithaviolencefarbeyondthescaleofanythingknowntohumans.1.WhatpuzzledChristiansenwhenhewasstudyingYellowstone?A.Itscomplicatedgeographicalfeatures.B.Itsever-lastinginfluenceontourism.C.Themysterioushistoryofthepark.D.Theexactlocationofthevolcano.2.Whatdoestheunderlinedword“bl