两颗人造卫星A、B绕地球做匀速圆周运动，周期之比为T_A:T_B=1:8，则轨道半径之比和运动速率之比分别为                    

A：R_A:R_B = 4:1，υ_A: υ_B ='1:2'

B：R_A:R_B =4:1，υ_A: υ_B =2:1

C：R_A:R_B =1:4，υ_A: υ_B ='1:2'

D：R_A:R_B =1:4，υ_A: υ_B =2:1