对于任意一个非零实数，它的倒数的倒数是它的本身．也就是说，连续施行两次倒数变换后又回到施行变换前的对象，我们把这样的变换称为回归变换．在中学数学范围内写出这样的变换（写对一个变换给2分，最多得4分） ．
相反数的相反数是它本身，集合A的补集的补集是它本身，一个复数的共轭的共轭是它本身，等等.
一个非零向量的反向量的反向量是它本身；一个命题的否命题的否命题是它本身；
一个函数的反函数的反函数是它本身。
阅读下面短文，掌握其大意，然后从20－40各题所给的A，B，C，D四个选项，选出可以填入空白处的最佳选项，并在答题卡上将该项涂黑。 The Great Wall of China The Great Wall of China is the longest wall in the world. It __21__from west to east,__22__ mountains, __23__ valleys and finally __24__ the sea. The Great Wall has a history of over two __25__ years. People began to __26__ the wall __27__ the Spring and Autumn Period in Chinese history. In about 221BC Qin Shihuang had all the walls __28__. __29__, the Great Wall came to the world. The Great Wall is __30__ 6,000 kilometers long, 6—7meters high and 4—5 meters wide. In most places it is __31__ enough for five horses or ten men to walk __32__ along the top. It was very __33__ to build __34__ a great wall in the old __35__.Thousands of men __36__ when they built it, The Great Wall was made not only of stones, but millions of __37__. Today, the Great Wall has become a place __38__ interest not only to the Chinese but also to people all over the world. __39__ the Egyptians feel proud of their pyramids, __40__ Chinese people also feel proud of our Great Wall.
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