The bird and the tree are friends．The bird often sings songs in the tree．Autumn comes．The bird has to fly to the south．Spring comes.The bird comes back，but she can’t see the tree．Grass tell her some workers cut the tree down and took him to a factory．Then the bird flies to the factory．The workers told her they cut the tree into wood．They used the wood to make matches．Then they took the matches to a village．The bird flies to the village and sees a girl used the last match to make the fire．The bird sings a sad song to the fire．

我国最早将货币统一成图样式的朝代是（    ）

关于函数f（x）=cosxsin2x，下列说法中正确的是____

①y=f（x）的图象关于（π，0）中心对称；②y=f（x）的图象关于直线x= $\frac{\pi }{2}$ 对称

③y=f（x）的最大值是 $\frac{\sqrt{3}}{2}$ ；         ④f（x）即是奇函数，又是周期函数．

2016年9月15日，中国成功发射天宫二号空间实验室，对其轨道进行控制、调整到距离地面高h=393km处与随后发射的神舟11号飞船成功对接，景海鹏和陈冬雨两名航天员进驻天宫二号．已知地球半径为R，地球表面重力加速度为g，当天宫二号在预定轨道正常运行时，下列描述正确的是（   ）