?? ????????????????????????
![](https://image.chezhanri.com/2020/0319/405d5f416fcb3fe17dba9a4e03628e01.png)
????:1????????????:?????????
2??????
3???????sn
4???????
5?????????
????6???????20? ?20?????,???
???????????:6??????????19???????,?????????,??????????
?????????,?????????????????????????????,?????????????????????????
???????????????????????????????,????????,???????????,????,???,?????????,????????????????,???????????,??????????????,????????????????????????
?,???????(?????????) ??:??????????????