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专四阅读理解练习11-20.doc

发布:2018-05-26约4.21万字共33页下载文档
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专四阅读理解练习Most earthquakes occur within the upper 15 miles of the earths surface. But earthquakes can and do occur at all depths to about 460 miles. Their number decreases as the depth increases. At about 460 miles one earthquake occurs only every few years. Near the surface earthquakes may run as hig
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