她在访问前对这座城市的历史先研究了一番。

She had boned up on the city's history before the visit.

《牛津词典》

最后，我们还需要确定整体数据访问策略——先检索什么数据，如何在每个源上过滤数据等。

And finally, we needed to determine our overall data access strategy — which data to retrieve first, how we would filter data at each source, etc.

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这两个函数均按照深度优先的顺序遍历树，但两者的差异在于先访问一个节点还是先访问其子节点。

Both functions walk the tree in depth-first order but they differ in whether a node is visited before or after its children.

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