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1·The thead element has a single child node, tr, with three children - all th elements.

thead元素只有一个子节点tr，后者有三个子节点—所有th元素。

2·In this instance, the table element is the root element, with two child nodes, thead and tbody.

在该例中，table元素是根元素，它有两个子节点，thead和tbody。

3·The paper introduces various kinds of methods on repairing damaged thead holes of mining and developing equipment in coalmines.

介绍了煤矿采掘设备破损螺纹孔的多种修理方法。