?? ???????????????
????:1??????????:??????
2??????vx
3?????????
4???????
5?????????
????????8?????????27?? (?)?????27?????,??8???21???7???
??,27???????12??20??,???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????36????400??,??????40??????;???????????????????????5??600?,??????????37???40??
??:???????????;?????????????????????????;?????????;????,??????,??;??????,??;?,???(??)
???:??????????????