单项选择题Priorto802.1w,Ciscoimplementedanumberofproprietaryenhancementsto802.1DtoimproveconvergenceinaLayer2network.Whichstatementiscorrect?()
A.Only UplinkFast and BackboneFast are specified in 802.1w;PortFast must be manually configured.
B.Only PortFast is specified in 802.1w;UplinkFast and BackboneFast must be manually configured.
C.None of the proprietary Cisco enhancements are specified in 802.1w.
D.PortFast,UplinkFast,and BackboneFast are specified in 802.1w.