阅读短文，从方框中选择适当的单词填空。

    The London Olympic Games is still a few months away. But in the US, kids had ____  in a mini-Olympics competition.
Michelle Obama（米歇尔.奥巴马）, the First Lady of the US, held the games. Children played basketball ____  four-time gold medalist(金牌得主) Lisa Leslie. They ____  played soccer and tennis with famous players. The ____  of the competition was to teach kids the Olympic spirit(精神).  “The most important thing is not to win, ____  to take part.” The First Lady said. How meaningful it is!

水池中有一个气泡由水底向水面运动，如果水的阻力和水中温度差异忽略不计，那么该气泡在到达水面前的运动情况是（    ）