若函数f（x）=$\sqrt{x^2-1}$+$\sqrt{a^2-x^2}$为偶函数且非奇函数，则实数a的取值范围为____ ．

我国民族的分布具有“____、____、____”的特点。

    Modern Chinese use the solar calendar（阳历）as English people do . But at the same time, they use their own lunar calendar. Each lunar year is given the name of one of these animals : the rat , the ox , the tiger , the hare , the dragon , the snake , the horse , the goat , the monkey , the chicken , the dog and the pig . This list lasts for 12 years and then starts again.

     Each Chinese month starts on the day of the new moon. And the full moon comes on the 15th day of the month. The New Year always starts between January 21 and February 20. On the last day of the lunar year, there is a big family dinner. All members of the family except married daughters try to be present at this meal, even of they have to travel many miles to reach the home of their parents. Old quarrels are forgotten, and everybody is happy. After the dinner, the children keep awake to welcome the New Year.

    The New Year celebrations last for 15 days, from the new moon to the full moon. On the first day, children and unmarried people go to visit their elder