After configuring FabricPath， the following appears in the syslog：  %STP-2-L2GW_BACKBONE_BLOCK： L2 Gateway Backbone port inconsistency blocking port port-channel100 on VLAN0010.  What is the cause of this message？ （）      

• A、 STP must be disabled； message indicates that STP is enabled.
• B、 STP is misconfigured； root guard must be disabled.
• C、 An inferior BPDU is received on a Cisco FabricPath edge port.
• D、 A superior BPDU is received on a Cisco FabricPath edge port.