a soft yellow malleable ductile (trivalent and univalent) metallic element; occurs mainly as nuggets in rocks and alluvial deposits; does not react with most chemicals but is attacked by chlorine and aqua regia
a unit of length used for distances within the solar system; equal to the mean distance between the Earth and the Sun (approximately 93 million miles or 150 million kilometers)
AU的用法和样例：
例句
It's my first week here so I'm not yet au fait with the system. 我刚来不到一个星期，对这里的制度还不太熟悉。
Au revoir, see you again next year! 再见，明年见！
We've got a German au pair for six months. 我们找到了一个可以干六个月的德国换工。
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