????:1???????????:??????

2????????

3????????????

4????????

5???sn??

????????????????????1??18?????(??????)???????????????????,??,???????????,??,?????

??????????????????? ?

1??????????????15?????????????18??????,“???????”???,?????????????????????????

??????????????,???,??????????,??????19?????????????????????,?????????????79???????;??9??15??????????

?????,??????????????,??????????,???????????????????????????????

???????????????????????????????????,??,????????????????????,?????????????,“????”?

“??”??????????,?????,??????????????,????,????????????,??(???)

??????????:????