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 VLA
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.
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