Which three statements about RSTP are true?（）
- ARSTP significantly reduces topology reconverging time after a link failure.
- BRSTP expends the STP port roles by adding the alternate and backup roles.
- CRSTP port satates are blocking,discarding,learing,or forwarding.
- DRSTP also uses the STP proprsal-agreement sequence.
- ERSTP use the same timer-baseed process as STP on point-to-point links.
- FRSTP provides a faster transition to the forwarding state on point-to-point links than STP does.