No one knows for sure why adolescence is unique ____ humans.

T℃时，向10L的密闭容器中同时充入6mol H₂和2molN₂，2min末测得生成NH₃ 1.2mol，前2min内用N₂表示的平均反应速率是____，H₂的转化率是____．

漫画《学步》的主要寓意是（    ）

18－10（＝）8 

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!