在二叉树中，哪种操作通常不涉及树的结构变化？

当使用GridBagConstraints的anchor属性为SOUTH，且组件高度小于显示区域时，下列哪种布局效果是正确的？

在英语写作中，哪种结构通常用于引入对比？

The seemingly effortless elegance of the dancer's performance masked years of rigorous training and meticulous attention to detail. This underscores that true mastery in any discipline often involves not only inherent talent but also a deep understanding of its underlying principles and a relentless dedication to the _____, despite their often being invisible to the casual observer.

在二维数组中，元素a[i][j]的直接前驱是？