单词拼写
黄浦江笑迎米奇，迪士尼情牵金猴。
It is fairly common in Africa for there______ a group of expert musicians surrounded by others who also join in the performances.
若{an}是一个各项都为正数的无穷递增等比数列，a1和a3是方程x2﹣5x+4=0的两个根，求此数列的通项公式an与前n项和Sn．
