A:where is his mother
B:where his mother is
C:where was his mother
D:where his mother was
(Ⅰ)求圆C的普通方程;
(Ⅱ)直线l的极坐标方程是 2ρsin(θ+π6)=53 ,射线 OM:θ=π6 与圆C的交点为O、P,与直线l的交点为Q,求线段PQ的长.
俾斯麦说“德国宪法的制定不仅仅是参照了英国的立宪制度,更重要的一点是得益于美国”,这主要表现在( )
根据以上实验事实判断: