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

2??????????

3???????

4????????sn

5?????

????10??18???? (??? ?)????“????????”18???

“????”???????120??“?????????????????????”??,??????????,????????????????????????????????????????????????????????????????????????????????;“??????”????????,???,???????

“?????????????”?????????(??)

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

??????????????,????200??????????“?????????????????????????????”??????????,??20????????????70????80????

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

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

?????,????“????”??“??????????”????????????25?????30????????????,?????????200?????????????????,???,100????,??????????“???????????????????????”??,??,??????????

???18????????????,?????????????????,???????????“????????????????????????????????????????”,???????????????????(??)

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