单项选择题
What does UDLD stand for？（）
A.UniDirectional Loop Detection B.Unspecified Distribution Label Detection C.Unified Distribution Label Direction D.UniDirectional Link Detection
单项选择题 WhatwillsignificantlydegradeDSLperformance，regardlessofDSLrateorlinelength？（）
单项选择题 ATMcarriesIPandPPPinformationwithATMcells.WhatATMadaptationLayerisusedwhenanATMcellcarriesIPpacketsandPPPframes？（）
多项选择题 WhichtwoofthefollowingaredesignatedfieldsforMACtunnelingprotocol（802.1ah）？（）
