We call this the vertical migration.

我们把这个叫做垂直迁移。

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So these animals have to travel from the ocean's depths toward its upper layers to feast on the phytoplankton growing there. We call this the vertical migration.

所以海底的这些动物要从海底游到海面来享用生长在海面的浮游生物，这被称为垂直迁移。

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People call them"the workers from farm". In theory we call this group"the rural-urban migration".

他们的地位显得很特殊，社会称此类群体为“农民工”，在理论上则称为农村进城务工人员。

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