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。
Earths Inner Core
Scientists have long struggled to understand what lies at the planets 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 Earths 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 Lehmanns inner core was composed mostly_____(55)iron. Since then,
Lehmanns discovery has_____(56)conventional Earth science.But now scientists are challenging traditional theory with new and radical _____(57) For example,Earths center could actually contain aninner 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 spheremay be the oldest fossil____(59)from the formation of Earth,says Dziewonski.
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