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.