Today, people are paying more and more attention to their health,         books on keeping healthy extremely hot.

A．to make

B．making

C．make

D．made

若两颗人造卫星A和B绕地球做匀速圆周运动，角速度之比为8∶1，则A和B两颗卫星的轨道半径之比为____________，运动的速率之比为_____________。