Which statement correctly describes the Cisco implementation of RSTP？ （）

• A、PortFast， UplinkFast， and BackboneFast specific configurations are ignored in Rapid PVST mode.
• B、RSTP is enabled globally and uses existing STP configuration.
• C、Root and alternative ports transition immediately to the forwarding state.
• D、Convergence is improved by using sub-second timers for the blocking， listening， learning， and forwarding port states.