These strategies have widely different characteristics with respect to migration effort and migration period, as shown in figure 1.

这些战略在迁移所需的工作量和迁移周期方面差异很大，见图 1。

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By looking at the fossil record from that period of time - before the Red Sea was formed - we can gain a clearer view of which species survived this great migration and which did not.

通过观察这一时期——红海形成之前——的化石记录，我们就能更清楚地知道哪些物种在这次大迁徙中活了下来，哪些没有。

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Rules on family migration (covering immigrants from outside the European Union) are entering a period of upheaval.

家庭迁移（从欧盟外的国家移入者）的规定进入了一个大的调整期。

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With a six month migration period ahead, developers and users may have hard choices to make.

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An earlier period of great migration came to an end, for example, when America some 90 years ago shut its doors to immigrants for a while.

ECONOMIST: Open up | The

Migration data for the most recent one-year period available, July 2010 t0 July 2011, show the Great Recession has shaken the rankings up quite a bit within the circle of fast-growth regions.

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