A train is a closed world.

火车是一个封闭的世界。

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Facebook is still very much a closed world of its own.

Facebook仍然是一个非常封闭的网络。

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Yet this world is not so closed as it seems.

然而，这个看似封闭的世界并不是滴水不漏的。

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Previously, my hometown was closed to the outside world.

以前，我的家乡与外界隔绝。

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Previously, my hometown was closed to the outside world.

以前，我的家乡与外界隔绝。

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