单项选择题
A.Enable bpduguard globally.
B.Enable rootguard.
C.Enable loopguard.
D.Enable spanning tree.
E.Enable UDLD
多项选择题 Youarethenetworkadministratorofamedium-sizedcompany，andusersarecomplainingthattheycannotsendemailstosomeorganizations.Duringyourtroubleshooting，younoticethatyourDNSMXrecordisblacklistedbyseveralpublicblacklistfilters.AfterclearingtheselistingsforyourIPaddress，andassumingthatyouremailserverhastherightvirusprotectioninplace，whataretwopossiblesolutionstopreventthisfromhappeninginthefuture？（）
单项选择题 AfterapplyinganewACLonadevice，itsCPUutilizationrosesignificantlyandmanymessagesstartingwith"%SEC-6-IPACCESSLOG"appearedontheSyslogserver.Whatcanbedonetoresolvethissituation？（）
单项选择题 WhichfeaturewouldpreventguestusersfromgainingnetworkaccessbyunplugginganIPphoneandconnectingalaptopcomputer？（）