A:to have puller dow
B:be pulled dow
C:pull dow
D:to have been pulled dow
如图,在Rt△ABC中,∠C=90°,AC=3.将其绕B点顺时针旋转一周,则分别以BA、BC为半径的圆形成一圆环.该圆环的面积为( )
选择最佳答案。