读甲、乙两地等高线图，完成下题

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!

正方形A₁B₁C₁O，A₂B₂C₂C₁，A₃B₃C₃C₂，…按如图所示的方式放置．点A₁，A₂，A₃，…和点C₁，C₂，C₃，…分别在直线 $y=kx+b$ (k＞0)和 $x$ 轴上，已知点B₁(1，1)，B₂(3，2)， 则B_n的坐标是____。