单项选择题
A.12m B.40m C.30m D.50m
A.12nmile;3nmile B.12nmile;4nmile C.25nmile;3nmile D.25nmile;4nmile
A.Ⅰ、Ⅱ 、Ⅳ B.Ⅱ C.Ⅰ~Ⅲ D.Ⅱ、Ⅳ