What is one of the reasons that custom QoS ACLs are recommended over automatic QoS when configuring ports on a Catalyst 6500 for use with IP phones？（）
- A 79xx IP phones do not automatically mark voice packets with non-zero DSCP values.
- B 79xx IP phones do not mark protocol packets such as DHCP， DNS， or TFTP with non-zero DSCP values.
- C 79xx IP phones do not mark voice packets with optimal DSCP values.
- D 79xx IP phones use a custom protocol to communicate CDP information to the switch.