You need to configure port security on switch R1.  Which two statements are true about this  technology？ （）

• A、 Port security can be configured for ports supporting VoIP.
• B、 With port security configured， four MAC addresses are allowed by default.
• C、 The network administrator must manually enter the MAC address for each device in order for  the switch to allow connectivity.
• D、  Withsecurity configured， only one MAC addresses is allowed by default.  
• E、 Port security cannot be configured for ports supporting VoIP.