单项选择题
A.Router A is the master virtual router， and Router B is the backup virtual router. When Router A fails， Router B will become the master virtual router. When Router A recovers， Router B will maintain the role of master virtual router.
B.Router A is the master virtual router， and Router B is the backup virtual router. When Router A fails， Router B will become the master virtual router. When Router A recovers， it will regain the master virtual router role.
C.Router B is the master virtual router， and Router A is the backup virtual router. When Router B fails， Router A will become the master virtual router. When Router B recovers， Router A will maintain the role of master virtual router.
D.Router B is the master virtual router， and Router A is the backup virtual router. When Router B fails， Router A will become the master virtual router. When Router B recovers， it will regain the master virtual router role.
单项选择题 Refer to the exhibit. Switch S2 contains the default configuration. Switches S1 and S3 both have had the command spanning-tree mode rapid-pvst issued on them. What will be the result？（）
单项选择题 WhichstatementiscorrectaboutRSTPportroles？（）
单项选择题 Refer to the exhibit. Based on the output of the show spanning-tree command， which statement is true？ （）
