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.