Asoftware-definedwideareanetwork（SD-WAN）isawideareanetworkthatusessoftware-definednetworktechnology,suchascommunicatingoverthelnternetusingoverlay（19）whichareencryptedwhendestinedforinternalorganizationlocations.sD-WANsimplifiesthemanagementandoperationofaVANbydecouplingthenetworkinghardwarefromits（20）mechanism.Thisconceptissimilartohowsoftware-definednetworkingimplements（21）technologytoimprovedatacentermanagementandoperation.AkeyapplicationofsD-WANistoallowcompaniestobuildhigher-performanceWANsusinglower-costandcommerciallyavailable（22）access,enablingbusinessestopartiallyorwhollyreplacemoreexpensiveprivateWANconnectiontechnologies.sD-WANtechnologysupports（23）ofService（QoE）byhavingapplication-levelawareness,givingbandwidthprioritytothemostcriticalapplications.
（19）
A．paths
B．routes
C．tunnels
D．pipes
（20）
A．adaption
B．security
C．updating
D．control
（21）
A．decentralized
B．automation
C．intelligent
D．virtualization
（22）
A．private
B．lnternet
C．internal
D．cross-domain
（23）
A．Quantity
B．Quality
C．Query
D．Queue