Which statement is correct about RSTP port roles？（）
- AThe designated port is the switch port on every nonroot bridge that is the chosen path to theroot bridge. There can be only one designated port on every switch. The designated portassumes the forwarding state in a stable active topology. All switches connected to a given segment listen to all BPDUs and determine the switch that will be the root switch for a particular segment.
- BThe disabled port is an additional switch port on the designated switch with a redundant link to the segment for which the switch is designated. A disabled port has a higher port ID than the disabled port on the designated switch. The disabled port assumes the discarding state in astable active topology.
- CThe backup port is a switch port that offers an alternate path toward the root bridge. The backup port assumes a discarding state in a stable， active topology. The backup port will be present on nondesignated switches and will make a transition to a designated port if the current designated path fails.
- DThe root port is the switch port on every nonroot bridge that is the chosen path to the root bridge. There can be only one root port on every switch. The root port assumes the forwarding state in a stable active topology.