题目

    Happy birthday! Do birthdays really make people happy? Of course they do. Birthdays celebrate the day we were born. Besides, that extra candle on the cake suggests another year of growth and maturity（成熟）---or so we hope. We all like to imagine that we’re getting wiser and not just older. Most of us enjoy seeing the miracle of growth in others, as well. For instance, seeing our children develop and learn new things makes us feel proud. For Americans, like people in most cultures, growing up is a wonderful process. But growing old? That’s a different story. Growing old 用平面分别截去四棱柱、圆柱、三棱锥、圆锥，截面形状是圆的几何体是圆柱和圆锥圆柱和圆锥．