Flurry tracked nearly 3 million active users of eBook apps in July, up from just around half a million in March.

Flurry在七月跟踪了电子书应用程序的300万名活跃用户，而这一数字在三月仅为50万。

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Researchers from the Albert Einstein College of Medicine in New York tracked the health of more than 500 elderly men and women for four-and-a-half years.

纽约艾尔·伯特·爱因斯坦医学院(albert Einstein College of Medicine)的研究人员在四年半时间里跟踪调查了500名以上老年男性和女性的健康状况。

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The National Center for Atmospheric Research in Boulder, Colo., has tracked half a century of declining rainfall on the continent.

科罗拉多博尔德美国大气研究中心(TheNational Center for Atmospheric Research)的跟踪数据显示，半个世纪以来非洲大陆的降雨日趋减少。

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The strongest tornado, rated a maximum EF5 on the Fujita Tornado Scale, tracked for nearly an hour and a half along a 38-mile path from Chickasha through south Oklahoma City and the suburbs of Bridge Creek, Newcastle, Moore, Midwest City and Del City.

CNN: Oklahoma City area was hammered by EF5 tornado in 1999