Traffic drop for FCoE is experienced across a Nexus 5548 switch. What is a possible cause？（）

• A、 Server’s CNA does not support DCBX and PFC TLV was not negotiated.
• B、 A "no-drop" class has not been configured for FCoE
• C、 The system is running with the default QOS policies.
• D、 The link is oversubscribed.