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 subsecond timers for the blocking, listening, learning,
and forwarding port states.

Explanation:
By default, a switch operates in Per-VLAN Spanning Tree Plus (PVST+) mode using
traditional
802.1D STP. Therefore, RSTP cannot be used until a different spanning-tree mode (MST or
RPVST+) is enabled. Remember that RSTP is just the underlying mechanism that a
spanning-tree mode can use to detect topology changes and converge a network into a
loop-free topology.
Reference:
http://www.cisco.com/en/US/tech/tk389/tk621/technologies_white_paper09186a0080094cfa.shtml