Refer to the exhibit. What is the effect when the switchport priority extend cos 3 command isconfigured on the switch port interface connected to the IP phone？（）

• A、Effectively， the trust boundary has been moved to the PC attached to the IP phone
• B、The computer is now establishing theCoS value and has effectively become the trust boundary
• C、The IP phone is enabled to override with aCoS value of 3 the existing CoS marking of the PCattached to the IP phone
• D、The switch will no longer tag incoming voice packets and will extend the trust boundary to thedistribution layer switch
• E、RTP will be used to negotiate aCoS value based upon bandwidth utilization on the link