单项选择题 What is one benefit of PVST+?（）

单项选择题 Refer to the exhibit. What switch proves the spanning-tree designated port role for the network segment that services the printers?（）

单项选择题 Refer to the exhibit.The network administrator normally establishes a telnet session with the switch from host A.However,host A is unavailable.The administrator′s attempt to the switch from host B fails,but pings to the other two hosts are successful.what is the issue?（）