The next two queries cannot use an index because an element "phone408" needs to be returned for every author, even if it is an empty element for authors outside the 408 area code.
下面两个查询不能使用索引，因为必须为每个author返回元素“phone408”，即使是区号408之外的author的空元素。
Spain ruled this large area including New Orleans until 1800, when the whole area was again returned to France, only to be sold to the United States in 1803.
西班牙便统治了这块包含新奥尔良在内的广大土地，一直到1800年，这时西班牙才又把整个区域归还给法国，不过在1803年却又卖给了美国。
The building will use solar energy to heat the pools and the interior area, and all backwash water is to be filtered and returned to the swimming pools.
建筑将采用太阳能加热游泳池和室内面积，而所有反冲洗水是经过过滤和回到泳池。
Other research in this area has required that cells of one type first be returned to a more generally undifferentiated stem cell state, which can introduce fresh problems.
该研究领域的其他技术都需要先将一种类型的细胞变回到普遍未经分化的干细胞状态，而干细胞才能发生分化。
Other research in this area has required that cells of one type first be returned to a more generally undifferentiated stem cell state, which can introduce fresh problems.
该研究领域的其他技术都需要先将一种类型的细胞变回到普遍未经分化的干细胞状态，而干细胞才能发生分化。
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