I have a chart here, which I'll make available to, with a listing of nations with worse literacy record in the world.

现在我手中有一张表格，这个我会公开给大家，这里列出了世界上,具有较差文化素养的一些国家。

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I don't have the data in front of me, so let's emphasize the difference between r1 and rf.

我现在手头没有具体数据，我们现在把目光转移到r1和rf的数值差上。

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Because the difference in the vector between two times is this vector.

因为两个不同时间点上矢量的差,就是这个矢量 ΔR

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