第6部分：完形填空(第5l～65題，每題1分，共1 5分)

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　　Earth’s Inner Core

　　Scientists have long struggled to understand what lies at the planet’s center， Direct

　　observation of its center is impossible，so researchers must_____(51)to other evidence．

　　In 1889，a German scientist detected a severe earthquake in Japan．Geophysicists concluded

　　that shock waves_____(52)jolts(晃動)from one side of Earth through the center to the

　　other side．Then in 1936，Danish geophysicist Inge Lehmann studied the waves______(53)

　　to determine that within Earth’s core of molten(熔化了的)iron lies a solid inner core-but_____

　　(54)that core was made of eluded(難倒)her．Other geophysicists quickly

　　determined that Lehmann’s inner core was composed mostly_____(55)iron. Since then，

　　Lehmann’s discovery has_____(56)conventional Earth science．

　　But now scientists are challenging traditional theory with new and radical _____(57)

　　For example，Earth’s center could actually contain an“inner core within the inner core，claim Ishii and colleague Adam Dziewonski．

　　Analyzing hundreds of thousands of earthquake wave _____(58)，they maintain that the inner core has at its heart a tiny， even more solid sphere(球體) . This sphere‘‘may be the oldest fossil____(59)from the formation of Earth，”says Dziewonski．

　　Dziewonski and Ishii speculate that shortly_____(60)  Earth formed around 4.8billion years ago，a giant asteroid(小行星)smashed into the young planet and nearly melted it. But Earth’s center didn’t quite melt;it______(61)mass as the planet cooled.  The core within a core may be the kernel(核心)that endured．“Its presence could change our basic ideas about the_____ (62)of the planet，”Dziewonski says idea is tame(溫和的)compared to the_____(63)theories of independent geophysicist J．Marvin Herndon．Earth’s inner core is made not of iron，he claims

　　but a_____(64)of nickel and silicon Hemdon has a truly revolutionary notion：Within the nickel silicide(硅化物)inner core is also an“inner”inner core—an 8 km—wide ball of the element uranium．Uranium is radioactive．Hemdon thinks the uranium releases heat energy as its atoms_____(65)fission-split and crash into another in a chain reaction. In other words，we may live on top of a gigantic， “natural”nuclear power plant.

　　51 A  try     B leave   C turn   D point

　　52 A  create   B  receive  C feel D overcome

　　53 A  work   B solution  C job D patterns

　　54 A whether  B what C why D how

　　55 A  from   B  within   C  of    D  to

　　56 A  followed  B  dominated   C  restored   D  opposed

　　57 A  ideas   B  demands  C  phenomena   D  movements

　　58 A things   B  acts  C  methods  D  records

　　59 A taken    B  benefited  C  left  D  kept

　　60 A after   B  before  C  since  D when

　　61 A expanded   B  modified  C  gained  D  melted

　　62 A size   B  origin  C  structure  D  shape

　　63 A radical   B  traditional  C  classical  D  conventional

　　64 A system   B  copy  C  model  D  compound

　　65 A charge   B  last  C  experience  D show