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