??12??????20????????(????????????????)??????????????????20????????

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

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

????????????????????????? ??????????????:???????? ??“??????”????

?? ????????

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

2?????vx

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

4??????

5?????600?????

??12??????20????????(????????????????)??????????????????20????????

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

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

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