天文工作者观测某行星的半径为R₁，自转周期为T₁，它有一颗卫星，轨道半径为R₂，绕行星公转周期为T₂．

则（1）该行星的平均密度为多大？

（2）要在此行星的赤道上发射一颗同步人造卫星，使其轨道在赤道上方，则该人造卫星的轨道半径为多大？

NAC’s (Network Access Control) role is to restrict network access to only compliant endpoints and (81) users. However, NAC is not a complete LAN (82) solution; additional proactive and (83) security measures must be implemented. Nevis is the first and only comprehensive LAN security solution that combines deep security processing of every packet at 100Gbps, ensuring a high level of security plus application availability and performance. Nevis integrates NAC as the first line of LAN security (84) In addition to NAC, enterprises need to implement role-based network access control as well as critical proactive security measures-real-time, multilevel (85) inspection and microsecond threat containment.

A．defense

B．intrusion

C．inbreak

D．protection