When the free electrons in a conductor move in one direction only. The current thus established is called a direct current, which is often abbreviated to DC.

当导体的自由电子只以一个方向运动时，这样产生的电流叫做直流电，常缩写为。

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DC has many wonderful, free museums and beautiful monuments to remind us of history.

华盛顿有令人惊叹的、免费的博物馆和能让我们回忆起历史的很漂亮的纪念碑。

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The yuan is still not a free-floating currency, and only seems to appreciate when tempers in Washington, DC, reach boiling point.

人民币还不是完全的浮动汇率，只有当华盛顿怒发冲冠时，才升值那么一点。

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Until then, tourists eager for free museum admission should bypass big cities for smaller, lesser-known ones, or otherwise target free and affordable options in big cities like the Smithsonian museums in Washington DC (which uniquely have free admission as a national trust).

BBC: Should museums be free?

Until then, tourists eager for free museum admission should bypass big cities for smaller, lesser-known ones, or otherwise target free and affordable options in big cities like the Smithsonian museums in Washington DC (which uniquely has free admission as a national trust).

BBC: Should museums be free?

On June 21st his bank became a plaintiff in a legal challenge brought with two free-market entities in Washington, DC, the Competitive Enterprise Institute and the 60 Plus Association, arguing that Dodd-Frank is unconstitutional.

ECONOMIST: A tiny Texas bank challenges Dodd-Frank