What are two reasons to implement H·323 gatekeepers？（）

• A、 to eliminate the need for VoIP gateways
• B、 to scale a VoIP installation with multiple gateways
• C、 to provide call admission control and limit the number of simultaneous calls on the network 
• D、 to meet the requirement to control H·323 gateways on a LAN
• E、 to accept call requests and reduce the load on the gateway