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

2?????????

3?????????

4?????sn

5?????????????

???????????1?????2??? 1??2?????????????,?,??45??

?????,????????????????????????45????????????,??????????????????,??,????,??????????????,????,???????????????????????????,??????,????????????45??????????,??,????????????????????????,???????????????

???????????,?????????45????45??,??????,??????????????????????????“?????????????”??????????,?????????????,?????????????????,??????

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