A:完全相同
B:完全不同
C:仅c(K+)相同
D:仅c(Cl-)相同
(I)求椭圆C的标准方程;
(II)若直线l′:y=﹣x+b交C于A,B两点,且PA⊥PB,求b的值.
The _______ class is at nine o'clock.
—Mom, I am hungry. —How about eating some _______?