气温上升发生在冬季和春季，而不是夏季。

The temperature increase has occurred during the winter and spring, not during the summer.

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由于寒冷的气温，冻土带有两层：最上面的一层被称为活动层，在冬季和春季被冻结，但在夏季解冻。

Because of the cold temperatures, the tundra has two layers: top layer, which is called the active layer, is frozen in the winter and spring, but thaws in the summer.

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这是结束的冬季和春季的开始。

It's the end of Winter and the beginning of Spring.

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