A:Ca
B:Fe
C:I
D:Mg
基因分离定律的实质是( )
Kitty's father will ____ the school cinema at ____ ____ two.
已知|AB|=2,动点P满足|PA|=2|PB|,试建立恰当的直角坐标系,动点P的轨迹方程为____.