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来源:雅诚德英语网
Keyssar uses these differential rates to help explain a phenomenon that has puzzled historians—the startlingly high rate of geographical mobility in the nineteenth-century United States.
Keyssar 利用这些不同的比率来帮助解释一个让历史学家困惑的现象——19世纪美国惊人的高地域流动性。