A.79xxIPphonesdonotautomaticallymarkvoicepacketswithnon-zeroDSCPvalues.
B.79xxIPphonesdonotmarkprotocolpacketssuchasDHCP，DNS，orTFTPwithnon-zero DSCPvalues.
C.79xxIPphonesdonotmarkvoicepacketswithoptimalDSCPvalues.
D.79xxIPphonesuseacustomprotocoltocommunicateCDPinformationtotheswitch.
正确答案：参考C
