题目

― Why do we have to walk to the station? And where is it?―     61    I guess．   Look! There’s a policeman! Ask him the way．― All right I’ll go and ask．―     62    ― Well，we have to walk down this road until we see a river on the right．Across the bridge over the river，we will be able to see some road signs which will tell us the way．―     63    How long does it take to walk there?― About fifteen minutes，if we walk quickly．    ― Fifteen minutes! We may be late for the train．And with these heavy bags，too! I think we ought to take如图，图1是由若干个相同的图形（图2）组成的美丽图案的一部分，图2中，图形的相关数据：半径OA=2cm，∠AOB=120°．则图2的周长为_____cm（结果保留π）．