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

2?????????

3???????

4??????????

5?????????

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

???????,???????????3.1???????????????,??????????????1.7??????????????,???????,????,????,?????

???,???????????????????????????????????????????????????????,????5??;???????????,?????????????????????????????

(??????????????? ??)

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