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The river formed the frontier between the land of the Saxons and that of the Danes.

这条河曾是撒克逊人与古斯堪的纳维亚人土地的分界线。

《牛津词典》

Famous explorers of the north American frontier, Lewis and Clark arrived at the mouth of the Columbia River on November 14, 1805, in nearly starved circumstances.

著名的北美探险先驱路易斯和克拉克于1805年11月14日在饥饿的情况下到达了哥伦比亚河的河口。

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Teddy Roosevelt, during his epic 1913-14 trip down the Amazon's uncharted River of Doubt, sought unbounded natural frontier.

WSJ: Riding Brazil's River of Doubt

And one of the many impediments to a long-mooted scheme to use the San Juan river for a second trans- ismithian canal is that it marks the frontier between Nicaragua and Costa Rica : efforts to patrol it frequently spark tension.

ECONOMIST: Border disputes