People of different countries and regions, different nationalities and cultures have formed with solidarity an Olympic family, ______they have deepened understanding and enhanced friendship.

计算：a²⁰¹⁷·（－a）²⁰¹⁶=____．

有关人口迁移与环境关系的正确叙述是  (      )

—Where is my pencil box? 

—It's ____（on/ in） your desk.

如图是X、Y两种元素的原子结构示意图，据图分析，下列判断错误的是（　　）

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