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1、2013年职称英语考试真题-理工类C级阅读判断第2部分：阅读判断(第16～22题，每题1分，共7分)下面的短文后列出了7个句子，请根据短文的内容对每个句子做出判断：如果该句提供的是正确信息，请选择A;如果该句提供的是错误信息，请选择B;如果该句的信息文中没有提及，请选择C。RadiocarbonDatingNowadaysscientistscananswermanyquestionsaboutthepastthroughatechniquecalledradiocarbon(放射性碳),orcarbon-14,dating.
2、Onekeytounderstandinghowandbysomethinghappenedistodiscoverwhenithappened.Radiocarbondatingwasdevelopedinthelate1940sbyphysicistWillardF.LibbyatheUniversityofChicago.Anatomofordinarycarbon,calledcarbon-12,hassixprotons(中子)andsixneutrons(质子)initsnucleus.Carbon-14,orC-
3、14,isaradioactive,unstableformofcarbonthathastwoextraneutrons(原子核).Itreturnstoamorestableformofcarbonthroughaprocesscalleddecay(衰减).Thisprocessinvolvesthelossofheextraneutronsandenergyfromthenucleus.InLibby'sradiocarbondatingtechnique,theweakradioactiveemissions(放射)
4、fromhisdecayprocessarecountedbyinstrumentssuchasaradiationdetectorandcounter.HedecayrateisusedtodeterminetheproportionofC-14atomsinthesamplebeingdated.Carbon-14isproducedintheEarth'satmospherewhennitrogen(氮)-14,orN-14,interactswithcosmicrays(宇宙射线).Scientistsbelieves
5、incetheEarthwasformed,themountofnitrogenintheatmospherehasremainedconstant.Consequently,C-14formationisthoughttooccurataconstantrate.NowtheratioofC-14toothercarbontomsintheatmosphereisknown.Mostscientistsagreethatthisratioisusefulfordatingitemsbacktoatleast50,000yea
6、rs.AlllifeonEarthismadeoforganicmolecules(分子)thatcontaincarbonatomscomingfromtheatmosphere.SoalllivingthingshaveaboutthesameratioofC-14atomstoothercarbonatomsintheirtissues(组织).Onceanorganism(有机体)diesittopstakingincarboninanyform,andtheC-14alreadypresentbeginstodeca
7、y.OvertimetheamountofC-14inthematerialdecreases,andtheratioofC-14toothercarbontomsgoesdown.Intermsofradiocarbondating,thefewerC-14atomsinasample,theolderthatsampleis.16Nowadaysmanyscientistsdependonradiocarbonfordatingage-oldobjectsARightBWrongCNotmentioned17Theradi
8、ocarbondatingtechniqueisonlyabout40yearsoldARightBWrongCNotmentioned18AnatomofordinarycarbonhassixprotonsandeightneutronsARightBWrongCNotm
