The swan was flying over a lake.

天鹅正在湖面上飞翔。

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He dreamed a black swan and several swallows flying in the sky.

他梦见一只黑天鹅和几只燕子在空中飞翔。

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The smaller the bird, for example, the more agile the flying — a swan may need the equivalent of two football fields to take off and get lift, while a hummingbird can rise like a helicopter.

例如，鸟类的体型越小，飞行动作就越灵敏——天鹅就需要两个足球场大的面积才能完成起飞和抬升动作，而蜂鸟就可以像直升机一样垂直起飞。

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