Which two statements are true about the function of CAC？（）

• A、CAC provides guaranteed voice quality on a link.
• B、CAC artificially limits the number of concurrent voice calls.
• C、CAC is used to control the amount of bandwidth that is taken by a call on a link.
• D、CAC prevents oversubscription of WAN resources that is caused by too much voice traffic.
• E、CAC allows an unlimited number of voice calls while severely restricting，if necessary，other forms of traffic.
• F、CAC solves voice congestion problems by using QoS to give priority to UDP traffic.