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

2???????sn

3??????????

4???????????

5??????????

6?13?,??,?????,??????????????????,???????????????????????????????????,????????????????????????????????????,????????“???”“???????????????”? ? ??? 6??13??????????????????,????????,????????????????????,???????????????,????????????????????????,?????,?????????????????“?”“?”? ???????? ? 6??13?,???,??????????,???????????????,?????????????????????????????,????????????????????,??“????????????????”“??”? ????????????????? ????????????????? 6??13??????????????,??,?????,??,??????????????,????,?“???”“??”? ?????????????? ????????? 6?13???,??????????????,?????????????????????,???,?????????????????????????,????,?“???????????????”“??”? ??? ?????????????? 6????????????????13?,????????,??????????????????????????????????,??,????????????????????????????????????,????????????????????????????????,????????“??”“??”? ?? ???????? ??????????????????:???