老师说:“摸一摸你的耳朵”,你应该说:
A:Touch your ear.
B:This is my ear.
— What does your mother do?
— She's a ____.
甲、乙两颗人造卫星均绕地球做匀速圆周运动,已知卫星甲的轨道半径为r,卫星乙的轨道半径为2r,若卫星乙的线速度大小为v,则卫星甲的线速度大小为( )