Lewis and Brooks argued that an important developmental milestone is reached when children become able to recognize themselves visually without the support of seeing contingent movement.

路易斯和布鲁克斯认为，当儿童不借助于观察偶然行为，也能通过视觉认出自己时，他们就达到了发育的一个重要里程碑。

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In fact, this milestone was reached only 10 months after the systems reached 200,000 total flight hours, and 22 months after the first 100,000 flight hours were accumulated.

事实上，“影子”无人机系统在达到首个100,000飞行小时22个月后，200,000飞行小时仅10个月后就实现了上述里程碑。

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The best time to ask is once you have achieved a goal or reached a milestone.

最好的时机是当你完成一个目标或者实现里程碑的时候。

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The milestone was reached yesterday when a Blu-ray version of the romantic comedy "Nick and Norah's Infinite Playlist" was delivered to Clay Shannon, a Netflix subscriber in Birmingham, Ala.

ENGADGET: Netflix notches 2 billionth delivery with a Blu-ray disc HD

It was not until after the Second World War that another milestone was reached - the first woman was nominated at the beginning of the 1946-7 session to the Chairman's Panel which allowed her to preside over a debate of the whole House in committee, which she did on 31 May 1948.

BBC: Women in parliament

If the milestone is never reached, or is reached, but too late, the acquirer pays nothing.

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