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?（）

多项选择题 Which two of these are characteristics of the 802.1Q protocol?（）

单项选择题 Based on the network shown in the graphic which option contains the potential networking problem and protocol or setting that can to prevent the problem?（）