Which statement is true about voice VLANs？ （）

• A、When the voice VLAN feature is enabled， all untagged voice and data traffic is sent through the voice VLAN.
• B、The voice VLAN feature is enabled by default.
• C、The IP phone overrides the priority of all incoming data traffic （tagged and untagged） and sets the CoS value to 0.
• D、The default CoS value is 1 for incoming voice and data traffic.