新东方网校：2012年职称英语考试理工类B级完型练习题2

　　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