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

2??????????

3???????sn

4?????vx

5???????????

12???27???22???,??????????

???????“????????????”????,??????????????????4???????????????????????,??????

???????????????4.3??????????????????,????40km/h,??60km/h?

??????????????,????????,??????????????,????,????????1.8?;????,?,??????????????,?,??????????????????2.7???

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