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 Earths center didnt 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.Earths 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 aninnerinner corean 8 kmwide 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, naturalnuclear 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 whyD how
55 A from B within C of D to
56 A followedB 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
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