Tom and I are good friends．Tom is an English boy，but I am a Chinese girl．He is 12 and I am 13．He is in Class One．I’m in Class One，too．
    Tom has a nice soccer ball．He can  play it very well．I have a computer．I can  play computer games，but I can’t play soccer．It is difficult．Tom teaches(教) me to play soccer，and I teach Tom to play  computer games．Now (现在) I can play soccer and Tom can play computer games．

在第53届苏州世乒赛女单决赛中，中国选手丁宁在0：2落后且右脚扭伤的情况下，“希望能战斗到最后”的强烈信念使她越战越勇，最终斩获冠军。丁宁的事迹告诉我们（    ）

如图，AB是⊙O的直径，C是⊙O上的一点，OD⊥BC于点D，AC=6，则OD的长为（     ）

Tom often goes to school ______ John. (      )