?? ?????????????????????????
????:1????????:????sn????
2??????????
3????????
4??????????
5?????????
??????1???2?? ??????,????,???,????????????????????????????
?????????????,??,????,????,??????????;????,???????????;?????????????????????,???????????????????????,???????????????????????????????????,?????????????
???????????????????????????????,??????,??????????????????,??,???????????,?????????????«??????????»«?????????»«???»??????,????,????????????????????;??;?????,?????????
????????????:????????