单项选择题
A.A
B.B
C.C
D.D
E.E
F.F
单项选择题 Whiletroubleshootinganetworkconnectivityproblem,atechnicianobservessteadylinklightsonboththeworkstationNICandtheswitchporttowhichtheworkstationisconnected.However,whenthepingcommandisissuedfromtheworkstation,theoutputmessage"Requesttimedout."isdisplayed.AtwhichlayeroftheOSImodeldoestheproblemmostlikelyexist?（）
多项选择题 WhichtwovaluesareusedbySpanningTreeProtocoltoelectarootbridge?(Choosetwo.)（）。
单项选择题 IntheimplementationofVLSMtechniquesonanetworkusingasingleClassCIPaddress,whichsubnetmaskisthemostefficientforpoint-to-pointseriallinks?（）
