When a BGP router is not capable of understanding 4-byte AS numbers， it will see 4-byte AS numbers as a special， reserved， 2-byte AS number in the AS path. Which 2-byte AS number is this reserved one？（）

A.a root port being transitioned to the blocking state
B.a port being assigned as a root port
C.a port being assigned as an alternate port
D.a root port being transitioned to the forwarding state

A.root port，designated port，alternate port，backup port，and disabled
B.standby port，alternate port，root port，and disabled
C.standby port，designated port，backup port，and disabled
D.root port，designated port，alternate port，and standby port