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.