A:正方形
B:长方形
C:圆形
D:三角形
如图,矩形ABCD中,E为边AD上的动点,将△ABE沿直线BE翻转成△A1BE,使平面A1BE⊥平面ABCD,则点A1的轨迹是( )
—Could you please me your notebook, Grace?
—Certainly. Here you are.