A:which wa
B:it wa
C:which were
D:them were
如图,斜面AC的坡度(CD与AD的比)为1:2,AC=3 5 米,坡顶有旗杆BC,旗杆顶端B点与A点有一条彩带相连.若AB=10米,则旗杆BC的高度为( )