You should tell _____ about it if _____ doesn't know it.
关于中纬西风带的叙述,正确的是( )①北半球为西南风②南半球为西南风③在中纬西风影响下降水较少④中纬西风由副热带高气压带流向副极地低气压带
(I)求出动点P的轨迹对应曲线C的标准方程;
(Ⅱ)一条纵截距为2的直线 l1 与曲线C交于P,Q两点,若以PQ直径的圆恰过原点,求出直线方程.