这种统一是指你不能拥有一个而不拥有另一个，它就像一块磁铁的南北两极。你不能拥有一个单极磁铁。
If you cannot have one without the other, it is like the north and south poles of a magnet.
相信经历过南北战争的美国人民，不难理解统一对一个国家多么重要和珍贵。
I trust it is not difficult for the American people, who went through the American Civil War in their history, to understand how important and valuable unity is to a nation.
美国铁路直到十九世纪八十年代才采用统一的轨幅，这就使得南北方铁路间的互连不但非常复杂而且缓慢、昂贵。
Railroads in the United States did not settle on a uniform gauge until the 1880s, making interconnections between lines in the North and South complicated, slow, and expensive.
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