8．设以卫星离地面高h处绕地球做匀速圆周运动，其动能为E_k1重力势能为E_p1,与该卫星等   质量的另一卫星在离地面高2h处绕地球做圆周运动其动能为E_k2，重力势能为E_p2则（    ）

       A．E_k1＜E_k2                                                                                        B．E_p1＜E_p2

              C．E_k1+E_p1＝E_k2+E_p2                                                                                                                             D．E_k1+E_p1＜E_k2+E_p2