Which three statements are true about the voice VLAN feature on a Catalyst 2950 switch？ （Choose three.）（）
A. The CoS value is trusted for 802.1p or 802.1q tagged traffic.
B. The voice VLAN feature is disabled by default.
C. The IP phone accepts the priority of all tagged and untagged traffic and sets the CoS value to 4.
D. When the voice VLAN feature is enabled， all untagged traffic is sent according to the default CoS priority of the port.
E. PortFast is automatically disabled when a voice VLAN is configured.
F. The default CoS value for incoming traffic is set to 0.
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