It has been frequently assumed, but not proved, that the majority of the migrants in what has come to be called the Great Migration came from rural areas and were motivated by two concurrent factors.

人们常常假设，但没有证据证明，在所谓的“大迁移”中，大多数移民来自农村地区，这是由两个同时发生的因素推动的。

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It has been shown experimentally that birds can align themselvesto their normal migration routes in blue light but have trouble doing so inyellow or red, so the link seemed worth pursuing.

实验表明，在蓝光中鸟类可以按照正常迁徙路线飞行，而在黄光或红光中则做不到，因此其中的关联值得探讨。

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Perhaps you see this as a risk also, but IBM has been providing migration paths for similar technologies for almost 30 years.

也许您将这也视为风险，但是IBM为类似的技术提供迁移路线已经有近30年时间了。

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But the slowed migration has significant political effect.

WSJ: Recession Slows Migration in U.S.

The numbers of African-Americans returning to the South are not as large as those seen during the Great Migration, but the trend has resonance because of the place the region occupies in black history and mythology.

CNN: Family roots lure many African-Americans back to South

The recession may have slowed the pace of net migration, but the essential pattern has remained in place.

FORBES: New Geographer