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

2?????vx

3?????150?

4?????

5?????????

??????????????????????9?????????????18? ???????????????????18?????,?????,9?16?20???????,?,??????

?,9???????????????????????16??????????????????????20?????????????,??????????????,???????????????????????(???????????????????)

?????????????,?????????????????????,??

????????????????,9???????16?20???,??,??(?????????????????)

?,9??????????21?????????????,???????????????????,???(???????)

????????:????????????????????