But once passed, it is gone forever.

而时间一旦度过，便永远地一去不返。

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He passed a cairn of stones that once had been a chimney, and a dry well covered with a slab of the tin so rusty it served as more warning than a safeguard.

他经过了一个曾经是烟囱的石冢，以及一口盖着生锈的锡板的枯井，井盖已经绣得与其说是一种防护，不如说是一种警告。

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Once the exams passed, everyone breathed a sigh of relief.

通过考试后，大家都松了一口气。

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President Kennedy once said: "I am certain that after the dust of centuries has passed over our cities, we,too,will be remembered not for our victories or defeats in battle or politics, but for our contribution to the human spirit."

VOA: special.2010.10.29

So whether we finish it today, or more likely when we finish it up on Friday, once we get passed isoelectronic atoms, that's it, that's all you need to study for this first exam.

因此，我们也许今天讲完，或者更有可能周五讲完，无论如何，就到我们讲完等电子原子为止，这是你们第一次考试所需要准备的全部内容。

麻省理工公开课 - 化学原理课程节选

Once passed, there is no automatic procedure to remove law unless repealed by Parliament.

BBC: 'Dead laws': Call to reform statute books

Once passed, they were now elevated to the rank of journeymen and could travel wherever there was work, practicing the craft.

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Once passed into law, they will be almost impossible to revoke.

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