单项选择题
Which of these Layer 2 access designs does not support VLAN extensions？（）
A.FlexLinks B.loop-free U C.looped square D.looped triangle E.loop-free inverted U
单项选择题 For acceptable voice calls, the packet error rate should be less than（）%
多项选择题 What are three primary activities in the cycle of building an enterprise security strategy?（）
多项选择题 Which two of these are recommended practices with trunks? （）
