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.