About 170 people _____ and dozens more _____ after a flood hit an Indonesian town last week.

A．were killed; are still missing

B．have been killed; were still missing

C．are killed; are still missing

D．had been killed; were still missing

已知地球半径为R，地球表面重力加速度为g，万有引力常量为G，现有一质量为m的卫星绕地球做匀速圆周运动，其轨道半径为r，求：

（1）地球的质量M

（2）卫星在轨道上做匀速圆周运动的周期