公民的基本义务又称为宪法义务，具有强制性的特点，拒不履行基本义务是违法行为，要承担相应的法律责任。你认为下列属于公民的基本义务的是（  ）

①维护国家统一和各民族团结        ②成年子女赡养扶助父母

③见义勇为                                        ④公民的人格不受侵犯

在平面解析几何中，当动点到一个定点的距离与它到一条定直线（定点不在定直线上）的距离之比是常数时，该动点的轨迹为圆锥曲线。常数的值不同，圆锥曲线的形状就不同。当常数小于1时，轨迹是椭圆；当常数等于1时，轨迹是抛物线；当常数大于1时，轨迹是双曲线。上述结论表明
①共性寓于个性之中 ②矛盾的同一性推动事物的发展 
③事物的量变引起质变 ④事物的联系是具体的、多样的

People in those days liked to believe in computers ________ the world.

Tom was not old, but he did not have much hair. His wife, Grace, had thick, beautiful, black hair. They had one daughter. Her name was Jane, and she was four and a half years old. There was a photo of her father in the living-room, and a few days ago, Jane looked at it for a long time and then said to her mother, “Mummy, why had Dad got very little hair? ”
Grace laughed and said, “He’s got very little hair because he thinks a lot, Jane. He’ s a clever man.”
Jane looked at her mother’s thick, black hair for a few seconds（秒钟）, and then she asked, “Mum, why have you got a lot of hair? ”

_____ deep down in the earth, the dead forests rotted away and became coal.