单项选择题
A. for multiple ISDN connections
B. for modem concentrated dial-up connections
C. for a group of users in the same vicinity sharing a connection
D. for use by mobile users
单项选择题 Whichroutingprotocolsupportsaflexibleareastructureusingroutinglevelsoneandtwo？（）
单项选择题 Whichsite-to-siteVPNsolutionallowsCiscorouters，PIXFirewalls，andCiscohardwareclientstoactasremoteVPNclientsinordertoreceivepredefinedsecuritypoliciesandconfiguration parametersfromtheVPNheadendatthecentralsite？（）
单项选择题 WhendesigningtheWANmodulewithintheenterpriseedge，whichdocumentisusedtospecify theconnectivityandperformanceagreementswiththeserviceprovider？（）