What does it mean if a backup is expired？（）
- A The backup set has exceeded the retention criteria set in RMAN and is eligible for removal.
- B The backup set has one or more invalid blocks in it and is not usable for recovery.
- C The backup set contains one or more tablespaces no longer in the database.
- D The backup set contains one or more missing backup set pieces.
- E The backup set is from a previous version of RMAN and was not upgraded.