Sub elements must be in pairs and correctly nested within their parent element.

位于父元素之内的子元素必须成对出现且使用正确的嵌套。

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A pylon is supposed to be a beautiful thing. In ancient Egypt, pairs of tapering stone towers called pylons marked the entrances of temples.

高塔应属美之物，在古埃及，成对下粗上细的塔门标出庙宇的入口，基督教建筑师也借用哥特教堂前面竖上双塔的想法。

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For instance, several name-value pairs could be included in the URL to perform more sophisticated operations.

例如，可以在URL中包括多个名称-值对以执行更复杂的操作。

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If I'm talking about two DNA strands and they differ only in one or two base pairs they won't be exact complements and they won't form this double helix.

假设有两条DNA单链,有一两个碱基不能配对,它们就不能完全互补,也无法形成双螺旋形结构

耶鲁公开课 - 生物医学工程探索课程节选

Scotland's home games will be in three pairs of matches played on consecutive days in May, July and August.

BBC: Scotland open CB40 with trip to Durham

They will be travelling in pairs.

BBC: Before the storm in Cameroon

The Chiterns Conservation Board said the area now had the highest breeding density of red kites in England and added there could be more than 600 breeding pairs in the area.

BBC: Cold March affects red kite breeding in the Chilterns