问题：

[多选] 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.