英语专业四级阅读理解冲关试题及答案2018年英语专业四级阅读理解冲关试题及答案Ifthouinjurestconscience,itwillhaveitsrevengeonthee.以下是小编为大家搜索整理的2018年英语专业四级阅读理解冲关试题及答案，希望能给大家带来帮助!更多精彩内容请及时关注我们应届毕业生考试网!Therearesomeearthphenomenayoucancounton,butthemagneticfield,somedayisnotofthem.Itfluctuatesinstrength,driftsfromitsaxis,andeveryfew100,000yearsundergo,dramaticpolarityreversal—aperiodwhennorthpolebecomessouthpoleandsouthpolebecomesnorthpole.Buthowisthefieldgenerated,andwhyisitsounstable?GroundbreakingresearchbytwoFrenchgeophysicistspromisestoshedsomelightonthemystery.Using80metersofdeepseasedimentcore,theyhaveobtainedmeasurementsofmagnetic?fieldintensitythatspan11polarityreversalsandfourmillionyears.Theanalysisrevealsthatintensityappearstofluctuatewithaclear,well?definedrhythm.Althoughthestrengthofthemagneticfieldvariesirregularlyduringtheshortterm,thereseemstobeaninevitablelongtermdeclineprecedingeachpolarityreversal.Whenthepolesflip—aprocessthattakesseveralhundredthousandyears—themagneticfieldrapidlyregainsitsstrengthandthecycleisrepeated.Theresultshavecausedastiramonggeophysicists.Themagneticfieldisthoughttooriginatefrommoltenironintheoutercore,3,000kilometersbeneaththeearth'ssurface.Bystudyingmineralgrainsfoundinmaterialrangingfromrockstoclayarticles,previousresearchershavealreadybeenabletoidentifyreversalsdatingback170millionyears,includingthemostrecentswitch730,000yearsago.Howandwhytheyoccur,however,hasbeenwidelydebated.Severaltheorieslinkpolarityflipstoexternaldisasterssuchasmeteorimpacts.ButPeterOlson,ageophysicistattheJohnsHopkinsUniversityinBaltimore,saysthisisunlikelyiftheFrenchresearchersareright.Infact,Olsonsaysintensitythatpredictablydeclinesfromonereversaltothenextcontradicts90percentofthemodelscurrentlyunderstudy.Iftheresultsprovetobevalidgeophysicistswillhaveanewtheorytoguidethemintheirquesttounderstandtheearth'sinnerphysics.Itcertainlypointsthedirectionforfutureresearch.?1.Whichofthefollowingtitlesismostappropriatetothepassage??A.PolarityReversal:AFantastic