?? ??????????????????4???
????:1???????v:?????
2??????
3??????????
4????????
5???????????
????12??????????20?????????? ????????????????????????20????,?????????????,“?????????????????????”?????????????????????,????????,??????“?????”???????????????
?????,???,???????????????????,????“?????????????”???????,????“??????????”????,?????????????????????????4??:???;?????????;??;?????
?????:?????