两颗人造卫星A，B绕地球作圆周运动，速度大小之比为V_A：V_B=2：l，则轨道半径之比和周期之比为（　　）

A．R_A：R_B=4：1    T_A：T_B=1：8

B．R_A：R_B=4：1    T_A：T_B=8：1

C．R_A：R_B=1：4     T_A：T_B=1：8

D．R_A：R_B=1：4    T_A：T_B=8：1

24.  Remember never to tell a lie to others. If you did, you would never ______it and it is more _____ that you will be discovered before long.

A．get away with; likely

B．get away from; possible

C．get away with; possibly

D．get away from; probable