【单选题】
The Company network administrator has entered the "auto qos voip cisco-phone" command on  switch R1. <br /> What does this command do？（）
A、It disables the trust boundary feature because the switch knows a Cisco IP phone is attached.
B、The switch assigns a CoS value of 5 to incoming packets.
C、If a Cisco IP phone is attached and removed， the switch continues to trust the CoS values as long as the switch is not rebooted.
D、It turns on STP to see if a Cisco IP phone is attached.
E、If a Cisco IP phone is attached， the switch trusts the CoS.
F、None of the other alternatives apply.
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