国家植树节基金会向许多城市发起挑战，要求它们通过种植和保护更多的树木来赢得那面“美国树城”的旗帜。

The National Arbor Day Foundation has challenged many cities to earn its "Tree City USA" flag by planting and protecting more trees.

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植树节起源于美国。

The Arbor Day originated in the United states.

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植树节起源于美国。

The Arbor Day originated in the United states.

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