Bruno was a boy of eight. His father worked in a cinema and his mother worked in a shop. He lived not far from his school. He always walked there and walked home. On his way to school, he had to pass a playground. It was very wet after it rained. One day,when he got home,his clothes were all wet. His mother became angry and said,” don't play in the water on your way home from school!”
    On the next day Bruno came back wet and dirty（脏的）clothes. His mother became even angrier.” I'll tell your father you come back wet again.” said his mother,” He'll punish you,you know.”
    The third day the little boy was dry when he came home.“you're a good boy today,” his mother said happily,”you didn't play in the water.”
   “No,” the boy said unhappily.” There were too many older boys in the water when I got there this afternoon. There wasn't any room（空地方） for me at all.”

冶炼技术在中国有着悠久的历史，下图表示了金属活动性顺序表中铜、锡、铁和铝元素被人类大规模开发、利用的大致年限：

函数f（x）=2a^x+1+3（a＞0且a≠1）的图象经过的定点坐标是____．

小明每天骑自行车或步行上学，他上学的路程为2800米，骑自行车的平均速度是步行平均速度的4倍，骑自行车比步行上学早到30分钟。设小明步行的平均速度为米每分钟，根据题议，下面列出的方程正确的是（   ）