The Arctic Circle is the boundary of this region of darkness.

北极圈就是这一黑暗地带的边界。

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Figure 1. The blue line represents the boundary of the clickable region.

图1：蓝色线框是可点击范围的边界。

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Figure 1. The blue line represents the boundary of the clickable region.

图1：蓝色线框是可点击范围的边界。

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