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

2??????vx

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

4??????????

5??????????

????12??18???? (??? ?)?????????????12?????18?????????

?,?????????????“??????????????????????,???”???,????????????????????????????????????????????18??????

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

??????????“???????????????”“????????????”“???”“??”4???????(???????????????) ????????????:??????????????????????