Compared to STP, RSTP protocol defines different port roles. For the description of the standby port and backup port in RSTP, which is correct? (Multiple selection)

Compared to STP, RSTP protocol defines different port roles. For the description of the standby port and backup port in RSTP, which is correct? (Multiple selection)
A . The port is prepared to back up the root port.
B . The backup port backs up the designated port.
C . The switch to which the backup port belongs is not the designated switch of the network segment to which the port is connected.
D . The switch to which the standby port belongs is the designated switch of the network segment to which the port is connected.

Answer: AB