王老师在一次“探究性学习”课中，设计了如下数表：

（1）请你分别观察a，b，c与n之间的关系，并用含自然数n（n＞1）的代数式表示：a=____ ，b=____ ，c=____ ．

（2）观察下列勾股数3²+4²=5²，5²+12²=13²，7²+24²=25²，9²+40²=41²，分析其中的规律，写出第五组勾股数____ ．

如图中，A﹣﹣E示意人体的不同结构层次，请据图分析回答下列问题．

金属和溶液在生产、生活中应用广泛

（1）工业上用磁铁矿炼铁的原理为____ ，其中高炉内加入焦炭的作用是____ ．

（2）农业生产中常用15%的食盐水来选种，现有50g质量分数为25%的氯化钠溶液，欲稀释为质量分数为15%的氯化钠溶液，需要加入水的质量为　____ ．

有关俄罗斯社会经济特征的叙述，正确的是（　　）

    December 25 is Christmas Day(圣诞节). Christmas is an important holiday in many countries. On Christmas Day, most families get together for a big dinner. They give presents to each other and visit friends. The Christmas tree is an important part of the Christmas holiday. Most families buy trees. The families decorate(装饰) the tree together. Parents usually tell their children that Father Christmas comes during the night and brings presents to good children. Of course, Father Christmas isn't real. The parents of the children are really "Father Christmas". They put the presents under the tree or into their children's stocking(长统袜) after the children go to sleep.