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

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。

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The page will use a Data Tree to display all of the states and cities in a hierarchical view.

此页面将会使用一个 Data Tree 在一个层次视图中显示所有的州和城市。

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With its world-famous landmarks such as the Eiffel Tower and the Arc DE Triomphe, and its wide, tree-lined streets, Paris is one of the most beautiful cities in the world.

拥有埃菲尔铁塔和凯旋门这样驰名于世的地标性建筑，以及绿树成荫的宽阔街道，巴黎不愧是世界上最美丽的城市之一。

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Replacing concrete with porous pavement, employing green roofs and rain barrels, restoring creeks and wetlands, and increasing tree cover can help cities absorb rain water rather than funnel it to sewer systems.

WHITEHOUSE: Building the Future: Innovative Water Infrastructure

The spring allergy capitals are based on tree pollen counts, while the fall cities are ranked on ragweed pollen counts from September through November of the previous years.

CNN: Worst U.S. cities for allergy sufferers

Tree-sellers scour distant mountainsides for older trees (though when uprooted and moved to cities many do not survive).

ECONOMIST: Plans to create greener cities are pruned