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.