before

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[b′f]〈副词〉，〈连接词〉，〈介词〉在…以前

He has never lost a book before．他以前从未丢过书。

Put everything back where it belongs before you leave．离开前把所有的东西都放回原处。

Aunt Wang will be back before nine．王阿姨会在9点前回来。