????:1???????????:??sn??

2????????

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

4?????

5?????

?????????????????????????12??2???????? (????????? ????????)???????????12?????????1?????????????«??????»(??????“???????”),?????????????????????????????????,?????????2?????????????????

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

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

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

?,???????,??????????????????????????,????????????????????3???????????????????;???????,???????????2?????

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