第6部分：完形填空  （第5l～65题，每题1分，共1 5分）
阅读下面的短文，文中有15处空白，每处空白给出了4个选项，请根据短文的内容从4个选项中选择1个最佳答案，涂在答题卡相应的位置上。
　
                          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（晃动）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（难倒）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（球体） . 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（温和的）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

答案:
51 C  turn to other evidence：寻求其他证据。Tum to属固定搭配。
52 A  create jolts：造成震动。其他几个选项意思不符。
53 D  wayes'patterns：波浪的形状。科学家通过研究震波的形状了解地球的情况。
54 B  此处的意思是地心是由什么构成的难倒了她。这里应使用what构成名词性从旬，作主语。
55 C  compose of：由……组成。固定短语。
56 B dominate：占统治地位，支配。Lehamann的发现在传统地球科学领域占统治地位。
57 A  此处的意思是：现在的科学家正用新的、激进的观点挑战传统的理论。本题只有填ideas才符合本句的意思。
58 D  此处填records，本句的意思是：通过分析数十万次地震波的记录，他们认为……。其他几个选项与句意不符。
59 C left：留下来的。此处的意思是：这一球体可能是地球形成时留下来的最古老的化石。
60 A  依据上下文，应用afte~句子意思才讲得通。
61 C  gain：获取。gained mass as the planet cooled：在星球（这里指地球）变冷的过程中，它逐渐获得了质量。
62 B  本文主要谈地球起源问题，故此处应填ongm.
63 A  本句前面出现的一个词是"tame"，与之对应，应该是"radical".
64 D  nickel和silicon的混合物，compound：混合物。
65 C  fission-split：裂变。经历裂变，用动词experience.