Anetworkisdeployedusingbestpracticesoftheenterprisecampusnetworkmodel，includinguserswithdesktopcomputersconnectedviaIPphones.GiventhatallcomponentsareQoS-capable，wherearethetwooptimallocationsfortrustboundariestobeconfiguredbythenetworkadministrator？（）

A.host

B.IPphone

C.accesslayerswitch

D.distributionlayerswitch

E.corelayerswitch