多项选择题 What two choices can you make when redundancy is required from a branch office to a regional office?（）

单项选择题 You are the Cisco Network Designer in Cisco.com. Which of these is a Layer 2 transport architecture that provides packet-based transmission optimized for data based on a dual ring topology?（）

单项选择题 You are the network consultant from Cisco.com. Please point out which Layer 2 access designs does not support VLAN extensions?（）